Grabbed by Holdem Manager
NL Holdem $1(BB)
SB ($31)
BB ($262)
UTG ($34.20)
Hero ($134)
CO ($222)
BTN ($29.32)
Dealt to Hero K♣ K♥
UTG calls $1, Hero raises to $4.50, fold, fold, fold, BB calls $3.50, fold
FLOP ($10.50) J♥ 2♥ 3♠
BB bets $7, Hero raises to $21, BB raises to $258 (AI), Hero calls $109 (AI)
TURN ($270) J♥ 2♥ 3♠ 7♦
RIVER ($270) J♥ 2♥ 3♠ 7♦ 4♣
Villain 21/13/ AF 4. wsd 21/ w$sd46. Donkey bet 25% of time.
Let's assume he would've pushed with a set (JJ, 33, 22), top pair + flush draw (J♥T♥ or better) and overpair (QQ), then you had ~44% equity, which is just enough to justify a call, given 5% rake :-)
If you exclude QQ from the above range (he would've probably raised it pre-flop), then your equity drops below 13%, easy fold.
Thus, unless you've reasons to suspect he would've pushed with a top pair (AJ) or overpair (QQ), I think it's better to fold.
I think i'd fold it, too.
If your hand didn't contain the K 
i would consider calling.
But since he can't have the K and the J♥ his FD- combinations are reduced since he can't have {A♥K♥, K♥Q♥, Q♥J♥, A♥J♥, J♥T♥, ...} your equity vs is range his bad.
You need 40% equity, and got:
Board: Jh 2h 3s
Dead:
equity win tie pots won pots tied
Hand 0: 34.158% 29.07% 05.09% 16692 2921.50 { KcKh, AJs }
Hand 1: 65.842% 60.75% 05.09% 34885 2921.50 { JJ, 33-22, AhQh, AJs, AcTc, AhTh, 9h8h, 8h7h }
Of course he could have more FDs in his range and donkbet less than 100% of his set-combinations, but he could also be donkbetting 30% of his setcombinations and 0% of his FD- combos (btw i already included AJs for some top pairs).
So i'd give him the benefit of the doubt and fold it
