Ive heard there is a book which can be bought in Stromgarde Keep, from which you can learn Fisrt Aid over 150. I cant find this npc. Is it correct that you buy this book in Stromgarde Keep???
You are correct about the alliance NPC in Stromgarde keep having the book. To find him, take a right once you get into the keep, and enter the "alliance area". Keep holding right, and you'll cross the bridge that you ride under on your way in. The vendor is in the courtyard on the other side of that bridge.
As best I remember he’s somewhat hidden by foliage. Until you turn to face him I think he’s hidden by a trellis. I’m thinking he must really be a rogue, as he’s very good at blending into his surroundings. I had difficulty seeing him the first time I went in search of the book.