Kill Jarko (you must loot the grimoire yourself) (be careful, he is strong), and take his Jarko's Grimoire.
Evil Alignment Option (Ogrimar):
Bring the book to Araknor, northwest of Lighthaven's temple, by saying the word grimoire.
This quest can be repeated indefinitely.
Rewards:

• 300 gold coins
  * Ring of Darkness or Ring of Confidence
  * You become Araknor the Necromancer’s apprentice (unlocks The Blind One’s spells on Raven’s Dust)
  

Note: You must wait 1 hour after someone has given the grimoire before you can submit it again.

Good Alignment Option (Artherk):
Bring the book to Lord Sunrock, the Mayor of WindHowl, by saying the word grimoire.
This quest can be repeated indefinitely.
Rewards:

• 300 gold coins
  * Gold Ring