Drakensang Online Wiki
 CLass master exmples are in the Kingshill regioin  these pictures can help u recognize their appearance and location 
here they are: 
Classmaster kingsill

Classmasters in Kingshill

Class Masters can be found in almost every urban section on the map. They occasionally give quests and can turn on/off PvP while out of the arena. Turning on PVP means that you can fight others who also turned on PVP while out of urban areas.