Jonas is located past the final room of the tusker assault. You can find him behind an invisible wall behind the alter in the final room of the tusker assault (the room with the Painbringer). If you give him one of the rusty worn keys you find on the tuskers within the dungeon he will reward you with 3million xp. If you give him other types of keys such as SIKs he will reward you with nanners, mastermage robes, and Nanner Island Portal gems(thats their name and they are worth 40k so they are different from the tusker island portal gems)