i managed to finish all the 6 quest you get in kaermorhen, in order to start the quest you need to go to talk to vesemir about finding the notes. then he tells you what to do next and the quest appears on the quest log.
Well it's weird the crafting scheme becomes available before you even got the Berengar's notes, stoping you from starting it... Losing the quest because some random loot already gave me the crafting scheme isn't nice