Speak to Tolfdir and choose “What was it you were missing?” if available. He seems to have lost his Alembic, which is an alchemic still (two vessels connected by a tube). You won’t get a quest marker, but oh well, here are the places I’ve found it so far:
- Top floor of the Hall of Attoinment, in the room directly across from the stairs, on top of a barrel.
- Top floor of the Hall of Countenance, in the chamber with the Arcane Enchanter, under a display case.
- Ground floor of the Hall of Countenance, in the room with the large cask, on top of a crate.
Once you've found it, return it to Tolfdir and he'll give you 30 Gold Coins and a Random Soul Gem filled. How nice of you, Tolfdir.