I thought I should make a reply on my own post. If you as myself live in Freeport, you can find the quest to become Warlock in North Freeport. The quest itself is located in the Magic Acedemy. You can do the quest already at lvl 18, which I did without any trouble. As a reward you get a staff, but I couldn´t use it before reaching lvl 19. Namora Ravenclaw