You need to go to Jordheim, the capital city of Midgard. Since you are a norse rogue, you probably started in Vasudheim. If that's where you are, then you'll see a big bridge at the outskirts of the town. Cross the bridge and go into the huge castle looking thingie and find either a hunter trainer or a shadowblade trainer, which won't be easy since it's a huge city, but it'll be good for you to explore since you'll have to go there a lot.
If you started in Mularn, then you'll see a big castle looking thingie in the distance. Go to it.
If you started in neither of those places, then you need to go to one of them.
If you started in Shrouded Isles, then ask someone around you to lead you to a hunter or shadowblade trainer.