Here´s another hand. What should I be betting on the river? no reads on the player

PokerStars No-Limit Hold'em, $0.02 BB (4 handed) - Poker-Stars Converter Tool from FlopTurnRiver.com

UTG ($5.84)
Button ($2.01)
Hero (SB) ($1.99)
BB ($3.08)

Preflop: Hero is SB with Q, 5
1 fold, Button calls $0.02, Hero calls $0.01, BB checks

Flop: ($0.06) 9, 7, 2 (3 players)
Hero bets $0.04, 1 fold, Button calls $0.04

Turn: ($0.14) 6 (2 players)
Hero bets $0.12, Button calls $0.12

River: ($0.38) K (2 players)
Hero ??