Talk to your characters, some will teach you how to became a Spirit healer, Assassin, Bard, Berserker, Arcane warrior and Shape-shifter those are all the ones I got from my party members. Some you buy books for.
Please tell me who to talk to, to become an arcane warrior? My mage is already a full on elementalist with 2 blood mage skills, but I want to be an arcane warrior mixed with a blood mage?