KTo is an awkward hand to flat the SB with pre but against a cutoff open I guess it's fine. It's a good hand to 3-bet as well though.
Check-call flop. Your lead doesn't make any sense - the flop is better for your opponents range (he has AK and KQ way more often than you do) and it's insanely hard to balance. Checking to the pre-flop aggressor should be absolutely standard at least up to 3-way pots. If you wanna put more money into the pot there'll quite likely be the option to check-raise, but your hand isn't strong enough for that here. With showdown value + added gutshot equity, check-call.
As played continuing turn is fine to charge draws and get value.
Check-call river though. Hard to get value at this point. As previously mentioned, this board just is better for a cutoff opening range than a SB flatting range. With the Tc you're blocking some bluffs which is a slight concern, but you're blocking JT as well. And there's only one king left, of course. As played it's a fold on the river, never are you ahead here.
Let this be a lesson that generally you shouldn't donk lead.