Talk to Ambrose. I am pretty sure you get it when you finish KT, no matter what level. If Headmaster doesn't have a quest, I don't know what you did wrong. :(
My highest wizard is a level 29 and i have finished Krok, WC, and Wysteria. Help? I'm out of breath from talking all day!
Have you gone and talked to Ambrose? Once you finish the last temple in Krokotopia you should of been able to go talk to Ambrose. worlds are not really by level but by quests lines. You have to finish certain questline to go to next.