To unlock the Champion trophy in FIFA 19, you will simply need to win a cup final in Kick Off mode.
To play a Cup Final:
- Go to Kick Off mode and choose a side with your controller > Advance
- Cup Final > Featured Cup Finals > UEFA Champions League
- Select the team and kits
If you're struggling to win the game, change the difficulty in Game Settings to a difficulty you can comfortably beat.
Win the match and the trophy will unlock, and you'll also unlock the trophy below as well: