Hi
Just finished this quest. The notes are like a spellbook you usually learn spells from (not like the research notes). Once you enter the level you go around in a clockwise fashion past hellhounds, then spiders and finally an undead ( can't remember which one...ghast or wight maybe). There are 2 small rooms near the center of the level but the demon is unable to see you. One room contains the spellbook pedestal.