opp is probably unknown(20/12/0 over 34 hands). Only one PSB left on the river. Is it too thin to bet anything on this river given that his range includes TT-QQ and lots of two pairs. However, we are up against an unknown and might lose some value if he checks back with worse hands.
No-Limit Hold'em, $1.00 BB (7 handed) - Hold'em Manager Converter Tool from FlopTurnRiver.com

SB ($27.50)
BB ($100)
Hero (UTG) ($108.65)
MP1 ($101.50)
MP2 ($54.90)
CO ($55.60)
Button ($100.20)

Preflop: Hero is UTG with K, K
Hero bets $4, MP1 calls $4, MP2 calls $4, 2 folds, SB calls $3.50, 1 fold

Flop: ($17) 2, 9, 7 (4 players)
SB checks, Hero bets $12, MP1 calls $12, 2 folds

Turn: ($41) Q (2 players)
Hero bets $25.50, MP1 calls $25.50

River: ($92) 10 (2 players)
Hero ?