Aesliip's Ring Location - Morrowind
Location: Caves of Fjalding (Solstheim)
Requirements: Complete all story quests up til The Skall Test of Strength
Aesliip's Ring is a powerful ring found in the Bloodmoon Expansion Pack and received as a reward during The Skaal Test of Strength Story Quest. There are quite a few quests you have to complete before reaching this one, for a full list check out the UESP wiki.
For this quest you'll need to go into the Caves of Fjalding under Fjalding Lake and find Aesliip inside Aesliip's Lair. Unless you are currently on this quest you will not find Aesliip in this dungeon. It doesn't matter if you choose to help Aesliip or kill him you'll get this ring as a reward either way.