Gotham Knights has collectibles that you will need both to defend Batman's identity and to unlock a trophy (or achievement). In particular, we are talking about the collectibles "Secret Identity Compromised". These become availablei after the mission "Main Case 01: The Last Case of Batman". They can be found at any time, so they aren't tied to specific missions, but you can take your time to find them, too during your free roaming raids.
The Compromised Secret Identity collectibles are marked as white icons on the map and to complete it you will need to interact with a terminal on the wall for placing false information on Bruce Wayne, so as to give him an alibi e protect the secret identity of the Dark Knight.
One of the difficulties that could test your skill is the fact that you have to do everything without being discovered by either the enemies or the security cameras, by nothing. In case you get caught you won't be able to access the collectible until the next night. There is a method to overcome this "problem": close the game and return to the main menu, so as to resume the attempt you were making. Obviously another method is to start a new night, so you can easily resume. And remember that to speed up the process you can also unlock the various Fast Travel points, in order to be even quicker in the process.
Location of collectibles Secret Identity Compromised
- Secret Identity Compromised 1 - West End: Available after "Batman's Last Case"
- Compromised Secret Identity 2 - West End
- Compromised Secret Identity 3 - Southside
- Compromised Secret Identity 4 - Old Gotham
- Compromised Secret Identity 5 - Financial District
Each time you get a collectible, return to the Bell Tower to bring up the next one. Of course, it is a rather cumbersome process, but it's a great challenge for the Gotham Knights.