Onmund's Request
In the Onmund's Request side quest, Onmund, a mage at the College of Winterhold will lament to you of a trade he made for his family's amulet. Speaking to Onmund will create a basic fetch quest through the radiant quest system.
Objectives
Walkthrough
After you speak to Onmund to start the quest you'll need to speak to Enthir. This will trigger a choice. You can try to persuade Enthir, but you'll need a fairly high speech skill to just persuade him to give the amulet back. Using the second option you can accept his request that you find The Grand Staff of Charming for him and he'll trade it back for the amulet.
The staff will be in the Boss chest (at the end of the dungeon or location) in one of the following locations (depending on where Enthir says):
It may also be in a chest in Broken Fang Cave (located Southeast of Rorikstead). There are only a couple vampires and skeletons that you will need to deal with. There are only two chests in the cave; it will be the one in the second room where the Master Vampire is.
After getting the staff return to Enthir and then the amulet back to Onmund. You'll gain a follower in Onmund if you so choose, but the only reward will be the loot you got from the staff's location.