Ring of Subjugation Walkthrough No Spoilers/Minor Spoiler Version

This god item is intended for mage characters, and therefore it would be advised for you to search for clues in the winterhold area, or perhaps along the road to winterhold. There should be a pair of journals in a satchel that has been lost, and this will contain the first clues to where you can find the required items for forging your god item.
Once you have obtained the contents of the satchel, you can either deduce the location of where you need to go next from either of the books. Deducing this from one book will take you directly to the dungeon that you need to go to. The other book will direct you to the general area of another journal, which in turn, will tell you the general location of the dungeon.
If you deduce the location of the dungeon directly: Your job is done. Once you find this dungeon, kill whatever lays there and take the items you need to forge your god item.
If you decide to find the second journal: This should take you to a major hold. However, the person you're looking for won't be there. He was old, and may have died nearby. His journal would be contained in another satchel in that area. This journal will give you the general direction of where you need to go to find the dungeon.
Once you've got the required items from that dungeon, as well as any other items you may need, you will need to forge said item. If you haven't figured it out already from any of the previous journals, I would recommend reading songs of the elves to find out where exactly you need to forge the god item.