What Richard said, plus:
The Riddermark's Finest
Action: Exhaust and Discard The Ridermark's finest to place 2 Progress Tokens on any Location.
Do you have to Exhaust him while questing, defending, attacking, or just Exhaust and Discard from play?
You can do this at any point that you can take an action. You must exhaust the character separate from any other action (e.g. he can't attack at the same time you're discarding him to use his text).