100NL, K9 two pairs might be good here ?

[pokerfan]

villain seemed an unknown donkish player over 30 hands. Get money in here good?
PokerStars No-Limit Hold'em, $1.00 BB (8 handed) - Poker-Stars Converter Tool from FlopTurnRiver.com

UTG+1 ($102.05)
MP1 ($60)
MP2 ($20)
Hero (CO) ($98.50)
Button ($64.10)
SB ($117.50)
BB ($120.90)
UTG ($105.50)

Preflop: Hero is CO with 9, K
4 folds, Hero raises to $3, 1 fold, SB calls $2.50, 1 fold

Flop: ($7) 10, K, 9 (2 players)
SB bets $5, Hero raises to $15.50, SB raises to $26, Hero ?

[wakeup]

whattt we have two pair vs a donk/unknown
get it in

[bearing]

This guy has hit 'raise' instantly after your raise.
In my experience this means they think they have you beat.
I may be inclined to fold this.
Or call and see what he does on turn, could be ak or kq thinking he is the nuts. On the turn I would take a check/small bet as confirmation you are ahead of him.