That will open the box and give you the Annihilator pistol. If you see the box that is circled above, look out the window directly in front of it and shoot the grey target with a pistol. To start the mission for Seraph, you will need to head to the location listed below in Firing Range.
You can find this in Supply Drops or off fallen enemies. To start the Prophet Character Mission you will need to find the Ocular Prosthetic. This is still kind of difficult, but it's much more doable than the previous version of the mission! Prophet Now, they've changed to you just having to kill 2 enemies without taking damage from them. It was really hard to do this because you had to get lucky in the people you killed, and hoped they were using Specialist characters. This used to be that you had to kill three Specialist characters in the game.