The Trials are available on the PS4 by loading a save or starting a new game, go to Options, and there is a new sub menu called trials.. you can only get to this menu in the game not on the main screen where you load your games.
If it's the same as with the Xbox and PC, you can tick on the Trials you want in the Gameplay Options.
Edit: That said - it seems you misunderstood the 'trials'. It aren't trials like in eg Dishonoured, but it are just gameplay options meant to make the game tougher.
The Trials are available on the PS4 by loading a save or starting a new game, go to Options, and there is a new sub menu called trials.. you can only get to this menu in the game not on the main screen where you load your games.
