Arniel's Endeavor is part of the College of Winterhold questline. You can start it by completing Arniel's Endeavor.
Objectives in order
Journal entry
Arniel has asked for more help with his project, though this time the request is very different. Enthir is apparently refusing to follow through on a trade; something Arniel needs for his work. He's asked that I go speak with Enthir on his behalf. Journal entry
Arniel asked me to deal with Enthir, who was supposedly refusing to complete a business arrangement. Enthir insists that he hasn't been paid, but will consider the deal done if I acquire a staff for him from Dungeon. Journal entry
I've managed to complete the trade agreement between Enthir and Arniel, and have the object Arniel was interested in. It's some sort of soul gem, though Enthir believes it to be useless. I should deliver it to Arniel. Journal entry
I've successfully completed a deal between Enthir and Arniel that is somehow related to Arniel's special project. He claims to be making progress, though I have no idea what that means.