This is part of the Operation Broken Eagle DLC.
You will find Dog Tags on fallen allies. These can be found during the main story, in side missions, and on the main map. Make sure not to forget to loot the Dog Tags after finding them, or killing the party that is carrying the Tag. It may sound a little like finding needles in a haystack, but fallen allies are always near red flares. If you see a red flare/red smoke, head towards it. You will not be able to obtain the final two Dog Tags until after you have picked up the GPS Tracker. A list of locations for the 11 Dog Tags are as follows:
1. Near the entrance to the subway at the start of the campaign.
2. First side mission in Sunset Hills.
3. West end of the northernmost bridge.
4. During the helicopter part of the campaign.
5. In the back of the strip club in south Almuda.
6. Southern gas station in south Almuda.
7. Small Chinese park area just off the highway in southern Ingleton
8. Outside of the yoga studio in southern Sunset Hills.
9. In the street at the southeast corner of Central City.
10. The rodeo type area in western Central City.
11. On the southernmost bridge between Almuda and Central City.
Note: All of these achievements in this DLC need to be completed prior to going to the Mayor's Mansion. After that point, you will not be able to obtain these achievements and you will be required to start a new campaign to do so.