I raise from the CO and both blinds call, then BB donks the flop. Was I right to call here, or should I ship it on the flop? Can I really fold to 4th spade on the turn given stack sizes?

Poker Stars $0.05/$0.10 No Limit Hold'em - 6 players
The Official 2+2 Hand Converter Powered By DeucesCracked.com

UTG: $5.90
MP: $10.20
Hero (CO): $14.90
BTN: $12.30
SB: $4.50
BB: $3.80

Pre Flop: ($0.15) Hero is CO with K 4
2 folds, Hero raises to $0.30, 1 fold, SB calls $0.25, BB calls $0.20

Flop: ($0.90) J 5 Q (3 players)
SB checks, BB bets $1, Hero calls $1, SB calls $1

Turn: ($3.90) 9 (3 players)
SB bets $1, BB raises to $2.50 all in, Hero raises to $13.60 all in, SB calls $2.20 all in

River: ($12.80) 4 (3 players - 3 are all in)

Raise flop, you have to protect your hand against A
Never slowplay flopped flush.

I don't raise K4s when there are two (loose) short-stackers in the blinds who are going to call with a really wide range. When your LP opens rate to get called by loose, short blinds incorporate hands like KTo, Q9s, ATo hands that can make a decent pair. K4s just isn't going to flop a hand we can go with against these guys very often, and neither is offering us the implied odds to play the hand when we do hit a gin flop (like 442 or AT3sss)

As played get this in on the flop, never slowplay your flopped flushes. The reason is because people are usually very eager to get it in on monotone boards with pair+FD hands or any decent card of the suit (in this case only the As is left but you get the idea). We are also going to play our sets (and usually 2pair) really fast on monotone boards to try and get max value from the pair+FD hands before a 4-flush hits so by playing our flopped flushes fast we balance our range.

Ship it on the flop raising k4s here is pretty marginal even for the biggest lag

Autoraise flop.

I also don't see how opening suited ks from the CO is bad especially if the button is tight. Might not be best with two mid stacks in the blinds though.

I'm not feeling good about raising from CO with K4s PF, even short handed. I'd raise it from the button for a blind steal if folded to me and the blinds are weak-folding nits.

As played, an easy all-in bet on the flop. You have no idea what the short stack is pushing here and you have 2nd nuts. You can't exactly wish for a better flop other than seeing the Ace of Spades.

Stop nut peddling and be more aggressive here.