Where is the second half of the rift rod in the cult of the eyeless quest?

Which half are you talking about?

One-half is with the Unseeing Eye's lair.
The other half you will be given by the avatar in the temple below the sewers.

spoiler alert


first you must talk to Tad. He will show you the way into the Unseeing Eye's lair. Go down there, and it is located in the most north-easterly room.

The eyeless thing has it. not on him, but with a stash of treasure and stuff. he appears right after you grab it, so be ready. if you pause the game, you can equip it and should be able to take out the bastard with one shot, plus help from your party members.