Section 1 – Wharf District
After kicking the gate open and engaging locust forces across, turn left and you should find a COG tag skull on the wall ahead. Go near it then enter the alcove to the left to find a COG tag under the bulletin board.
Section 2 – Parade Grounds
D. Yalovsky, SPC, Halvo Bay
Exit the hotel and proceed along the street. You should find a COG tag skull on the wall beside the stairs of the building to the right. Take the stairs and go around to the right to find the COG tag on the balcony.
Section 3 – Upper State Street
As you make your way to the ruined building where the declassify mission skull is, you should see a COG tag skull on the broken wall to the left. Check the big pile of rubble to the left to find the COG Tag there.
Section 4 – State Street Rooftops
After taking out the Reaver, you have to cross the plank to the next building. Before doing that, you should spot a COG tag skull along the way. Go up the ramp beside the plank and find the COG tag on the floor behind the vent.
Section 5 – First Avenue Rooftops
S. Bishop, COL, Gerrenhalt
At the start of the mission, look to the left to find a COG tag skull. Check the corner past it to find the section's COG tag.
Section 6 – Museum Square Rooftops
The COG tag is located to the left side of the rooftops, behind some sandbags beside the stairs so if you're planning to maximize your time, I suggest starting the section without the declassify mission, get the COG tag and restart the section so you can concentrate on the declassify mission.
Section 7 – Overlook
Getting this section's COG tag is a bit tricky. You have to wait for second wave to arrive since they'll be coming in from the door across the stairs where you found the last section's COG tag. You have to enter that door and you'll find the COG tag inside.