The Achievement can be obtained after you have killed Plant 42 at the Residence Building and returned to the Mansion with the Helmet Key.
In order to obtain the "Last Book Vol.2" you will have to make your way to the Library (Mansion Map 2F West Side).
Start from the Medical Storage Save Room (Mansion Map 1F West Side) and make you way upstairs. Run through the area where you found the Arrow, past the Crimson Head Zombie and through the door that leads upstairs to the Knights Armour Puzzle.
Run to the end of the narrow corridor and unlock the door (Helmet Key) leading to the upper section of the Library and follow it to the end.
BOSS FIGHT: YAWN (Round 2)
Easy way to kill Yawn is to use your Combat Shotgun and keep running in circles around the bookshelf. Run, stop, shoot, run stop, shoot... should do the job nice and easy.
After you have killed Yawn you can go behind the bookshelf and pick up the book.
Achievement unlocked