Alter Aeon Online Help

Keywords are:  'necromancer skill summon demonic tutor'

Skill: demonic tutor            Lvl 29 Necr  (85%)
                                (critical)   Requires: demon lore
                                Group: Necromancer Demonlore

Usage:
summon demon [soulstone] tutor <spell name>

Once you've mastered demonic favor, you can summon a demon to give you
arcane magical knowledge.  Learning spells with a demonic tutor requires
practices just like practicing the spell normally.  It can sometimes be
easier to take the risk and learn from a demon than to scour the
material plane looking for ancient spellbooks.

There are also some necromancer spells that can only be learned from
demons.