I dont think there is a button in that interface to open the spell book. So you need to type /book
or make a hotkey that has /book in it
or go to the options screen in EQ and remap a key to open the book
(I have B remaped to open my spell book).
I dont know if you already know this but the /book command is pritty nice. You can type /book 4 and it will open the spell book on page 4.