Hand reading exercise and river action

[Aces McGee]

Hi guys

Here's a hand I played in one of my first two orbits at a Party $3/$6 table. I think it could be a very good hand reading exercise. Hopefully someone will find this useful.

Unfortunately, because this was one of the first hands I played at the table, I don't have any reads for you.

UTG and UTG+1 both limp. It folds to me in the hijack and I raise 9d9c. The blinds get out the way and we take the flop three-handed.

The flop is 6d 5c 3d.

They both check to me, and I bet. UTG calls, UTG+1 now raises. I 3-bet. UTG calls, UTG+1 caps, we both call. 3 players to the turn for ~9 BB.

The turn is the Qc. UTG checks, UTG+1 (flop capper) checks, and I bet. Both call.

River is the 9h. UTG checks, UTG+1 bets.

What does UTG+1 have? What should I do on the river with my set of nines?

Post your reasoning.

-McGee