Nightblood Mastery

Location 1: Rivervale

From the docks in the Enchanted Lands you need to head to Rivervale. Its a short run, roughly to the east. You'll see a rope bridge heading up to the mountain, with a halfling guard standing at the base of it.

Once inside look for this building called "The Loom" at around -180, x, -25:

Inside you can find the book by searching the shelves: