Welcome to the community @DaSimzter. 
The Watch Dogs 2 trainer has specific instructions you need to follow in order to be able to use the game with the trainer.
Please make sure you are following the instructions that are included in the trainer. If you are not following the instructions correctly then the game will not launch with the trainer injected correctly. You’ll find these instructions in the Notes panel, which us underneath the Play button in the trainer.
If you got the game for free from Uplay recently, then this is the instruction:
If the first sentence doesn’t work, try the custom launch parameter and then try this: 32 bit and 64 bit.