How To Earn Not A Scratch TrophyFirst you need to get to Memory Sequence 8. When you reach the end of it, you’ll watch a cutscene and end up in a large building with enemies slowly approaching you. Walk across the tightrope, and hide behind the green door.
Starting from the top floor is the best way to do this. You’ll see two patroling enemies and one that is looking down into the atrium. Wait for the patrolmen to turn their backs to you, then slide-assassinate them one by one. When you kill the third one, drop down onto the beams below using the ledge.
When the patrolmen have their backs agains the wall, drop down and assasinate the first, run towards the other end of the room (killing the guard in the middle), then get the last one before he can alarm the others.
The ground floor should be easy, as there’s only one enemy there. If you haven’t taken any damage, once you kill him, you’ll unlock the Not A Scratch trophy/guide.
Here’s a video showing the process: