Tough situation. I feel like calling, raising, and folding all suck here.

It kinda seems like a reverse implied odds hand since you have absolutely no reads on the opponent. I think folding is a mistake, but I don't think its that big of a mistake.

If CO is a decent player, he probably would be raising AK, KQ and KJ, maybe KT instead of limping behind. This increases the likelyhood that the CO is a bad player and is limping worse kings.

I think check-calling allows your opponent to play the widest range here, and hopefully will try and bluff you with a mid pocket pair that thinks you are just taking a stab at the pot. You probably aren't getting max value, but I think it allows you to control the size of the pot to a good degree.