Ghost Mastery

Location 1: Nektulos Forest

First you need to get to Nektropos Castle. To do this you must have completed the mastery quest for it. Head to the northeast area of the zone to get to Nektulos Castle.

Location 2: Nektropos Castle

From here you just head straight forward to a set of two doors.

Take the door on the left, and you will enter a room with a fallen staircase. Walk into this room and turn right, and you should see another door past the staircase:

Walk into this door, and on your left you will see a pair of double doors.

Walk through them to enter a bedroom. Inside here you should be able to get the book from this closet:

Just as I was making this guide however, I read an email from someone saying they got the book from a stack of books laying next to a bed. Now, I don't know if they are two spawns in the same room which each give the book, two spawns in different rooms, or if the patch changed the location of the book, but I did get my Ghost book from this book closet.