Firstly, Diana Allers is in the Passenger Lounge of the Normandy dock (look into your map) Speak to her and you can allow her to come onto your ship. You can romance her later in the game and she also is a War Asset.
Go left after you enter the embassies and you should see a Volus talking to a Human and a Turin to the right. Listen to him to get this.
Go to the Shrike Abyssal star system which is shown on the galaxy map after you do the quest Priority: Palaven. Go to the sub system Urla Rast and you can find the artifact on the planet Talis Fai. Get back to the Volus after you have it.
You should be able to see a guy - Osoba talking on his phone to the left as you come to the Embassies. Speak to him to get this quest.
You can pick it up while doing the quest, Tuchanka: Turian Platoon, refer here - main page for more information on that. If you missed it doring that mission then you can just buy it from Specter Requisitions in the Procurement Terminal in Normandy's Shuttle Bay. GO speak to the father after that.
You can meen Jondum Bau a Salarian who's standing to the right of the C-Sec office in the Embassies area. Speak to him to get this quest and you also get a chance to meet an old friend.
After accepting to do this, go into the specter office and look at the specter terminal. You should see a message "Hanar Embassy Tracking", enable it. Now, open your map and you'll see a "Terminal" listed in the points of interest. Go to the terminal which is in the office suites. Now, you need to go to the next Terminal which is in the Docks Holding Area, again, look into your map for clarity the Terminal is in the Security Checkpoint. Go to Bay E28 in this area (map) and then back to the security checkpoint. After all that, we have a loction. Go back to the offices in the Embassies and speak to Bau. EVerything that follows is a cutscene...
After you enter the hospital, look to the left and you'll see a doctor speaking on the phone, approach her to get this. Or you may already have got this while doing the N7: Cerberus Lab mission when you took the medi-gel formula. If you did not pick up the formula during that mission then just buy the formula from Specter Requisitions in the Specter office in the Embassies. You can also access Specter Requisitions on the Procurement Terminal in the Normandy's Shuttle Bay. Just give the formula to the doctor to end this task.
You can pick up the Medi-Gel formula while doing the quest N7: Cerberus Lab. Refer - main page and read the mission for the exact location. Even if you missed it during the mission you can still buy it from Specter Requisitions in the Procurement Terminal in the Shuttle Bay of The Normandy. Give it to the Asari to end this task.
As you enter the second part of the Hospital in the area between Lab Services and Inpatient Wing you can hear an Asari Scientist to the right. Hear her to get this quest.
You can pick up the interfaces from the mission - Grissom Academy: Investigation, visit here for more info - main page
If you did not pick up the formula during that mission then just buy the formula from Specter Requisitions in the Specter office in the Embassies. You can also access Specter Requisitions on the Procurement Terminal in the Normandy's Shuttle Bay. Give it to the scientis to end this task.
There's a woman on a call outside the Purgatory Bar, listen to her to get this. You can get them during the mission N7: Cerberus Attacks visit - main page - and read there for more info. Even if you miss it during that mission you can still buy it from the Specter Requisitions in the Procurement Terminal in the Shuttle Bay of Normandy. Go back to the woman & give the Grid Schematics.
Go to the Docks Holding Area to meet Darner Vosque, he's near Cargo Hold A (look at your map). You can choose to kill the General or to work things out with him. After that, go to the Commons and to the General (he's shown in the map). If you don't remember him, he was giving trouble to the Asari Consort in Mass Effect the first part. You can give out an order to kill him or be friendy with him. If you are friendly then go to the Meridian Market Place and speak to the left most Salarian and agree to his demands. You can find what the Salarian wants in Kite's Nest and Sub-System Vular. Look in the planet Vana to get it. Go back to the Salarian and the General to finish this.
Go to Bailey in the C-Sec office on the Embassies. After you speak to him he agrees to set up a vid comm with the Asari. After speaking to her, you can release her or find another way. If you want to find another way, then go to the Docks Holding are and look for Sayn (in your map). Talk to him and ask him to grow a pair.
Go back and speak to Aria after you do all the baove three quests just for formality.
Listen to the Salarian outside the C-Sec office in the Commons area.
You can buy these from the Specter Requsitions in the Procurement Terminal in the Shittle Bay of the Normandy after the mission N7: Ceberus Fighter Base, for more info on that mission Visit - main page.
Speak to Liara in the Commons area (look into your map) and if you have been nice to her, she asks you to talk to Barla Von. He's to the left as you exit the elevator in the Bank area.
You'll have to wait for the Krogan DMZ shows up on the Galaxy Map which happens after Priority: Sur'Kesh. Go into the DMZ and find the planet Rothla in the system Dranek. Scan the planet to get the asset. Go back to Barla Von to finish this task. Krogan Dying Message
You will get this quest during the mission Tuchanka: The Rachni when you pick up an audio log from a dead krogan.
The following are after the mission Priority: The Citadel where you save the council.
There's a Turian on the phone past the Specter Office to the right. Listen to him to get this.
The Ceberus Ciphers can be picked up during the mission N7: Communications Hub. If you miss it then just buy the Ciphers from the Specter Requsitions from the Procurement Terminal in the Shuttle Bay of the Normandy.
You will see an Asari War Scientist in the Embassy Offices area in the Embassies.
The Reaper Code Fragments can be picked up during the mission Rannoch: Geth Fighter Squadrons. If you miss it then just buy the Ciphers from the Specter Requsitions from the Procurement Terminal in the Shuttle Bay of the Normandy.
In the Hospital area, as you move from Lab Services to the Inpatient Wing, you can see two rooms, one to the left and the right. Go into the left room to get this.
The Chemical Treatment can be picked up during the mission N7: Fuel Reactors. If you miss it then just buy the artifact from the Specter Requsitions from the Procurement Terminal in the Shuttle Bay of the Normandy.
In the room opposite of where Ashley/Kaidan was kept earlier is a salarian doctor, listen to him.
The Turian Poison can be picked up during the mission Arrae: Cerberus Scientists. If you miss it then just buy the artifact from the Specter Requsitions from the Procurement Terminal in the Shuttle Bay of the Normandy.
You should see a Turian to the left od Appolo's Cafe in the Commons area.
The Target Jamming Technology can be picked up during the mission Rannoch: Admiral Koris. If you miss it then just buy the Technology from the Specter Requsitions from the Procurement Terminal in the Shuttle Bay of the Normandy.
To the left of the C-Sec office in the Commons area is officer Noles. Speak to her to get this task.
Go to the Specter Office and use the Terminal and Authorize this. Next to the hospital and the Lab Services area, you should see the console as you walk around here. The next console is in the Normandy Dock in the Passenger Lounge. Bay E28 of the Docks: Holding Area has the last console.
You can get this after you read a mail o your private terminal on the Normandy
First Authorize the tracking of the Ambassidor from the Specter Terminal in the Specter Office in the Embassies area of the Citadel. Follow the locations on your map next, just look into your map and see if any new points of interest are shown in any level of the CItadel. You will need to go and speak with the Guard outside the Offices are in the Embassies. Check everything on the terminal and pick up the bug from the left of the room here. Then go to the Apartments area in the Commons. Go left up the stairs and into the last room.
The following are after the mission Priority: Mars and when you get back to the Normandy from the Citadel, you can check these out.
You can scan by going into a solar system and hitting the scan button. Sometimes scans show up, fuel wreckages and other times, important things like War Assets and Artifacts needed to complete the tasks which you get on the Citadel.
Here's a video of a scanning I did -
NOTE: ARTIFACTS ARE NEEDED TO COMPLETE TASKS FROM THE CITADEL...
This only shows if you accept the mission Citadel: Barla Von
Fuel Wreckage -
The following is after you do any mission after Priority: Sur'Kesh or after the mission Attican Traverse: The Rachni, Specialist Traynor mentions a cerberus abuction and then you get a quest and this place shows in the galaxy map.
Avid, excessive, convoluted, harcore, intrinsic, addicted gamer who only plays games...
believe me, there cannot be a better description of me than that.... (I'd probably take that onto my gravestone)