Don't know if this has been brought up elsewhere, but there is a WQ in Stormheim, Beasts of Burden, where you need to defeat Andurs and Rydyr. As long as you don't complete both objectives, you can farm one fight and get XP. With both pet treats and hat, I'm getting roughly 4800 xp at 23-24 levels and ~7000 at 14 (this is lowest pet I had).
Edit. Andurs fight is preferred. Just let the leveling pet hit once/or pass. Swap to Ikky, Black Claw, Flock. And that's it!