Final Stand Dog Tags and Phantom Assignments
1) They usually spawn few minutes after someone picks them up. The location is random every time though.
2) About Phantom assignments, you need to complete all the assignments in order (Prospect-->Trainee-->Initiate-->Operative). First 3 assignments require a password to be activated. You have to click a small skull in bottom left corner of leaderboards page and then type a password. For Prospect it's bumpinthenight (see this link for instructions http://www.primagames.com/games/battlefield-4/video_strategy/battlefield-4-phantom-prospect-easter-egg-assignment ) for Trainee it's epic dream worlds (see this link http://www.primagames.com/games/battlefield-4/video_strategy/how-unlock-battlefield-4-phantom-trainee-assignment ), for Initiate it's 24344241893 (see this link http://www.primagames.com/games/battlefield-4/tips/battlefield-4-phantom-initiate-password-and-how-complete-assignment).
Once you are done with these assignments you will be able to start working on Phantom Operative. From what I heard you cannot get the dogtags until you complete the first 3 assignments. This video describes the whole Phantom Operative walkthrough. https://www.youtube.com/watch?v=g4azB6iQGOA
