[retrac]

A quick survey of my communications finds "OK" to be the most common neutral acknowledgement used by both myself and my peers of millennial and Z-age. (Older milennial here.) "kk" is, by my reading, not appropriate for work. That's how you text your friend, or even intimate partner. Cutesy and far too intimate.

But if someone said "kk" I would assume an idiolect difference, not trying to prognosticate deep meaning behind it, barring other clues like chocolates. Making such inferences -- which are based on a sample of highly subjective and constantly changing idiolects which probably do not have anything approaching consensus -- is kinda setting yourself up to fail. Miscommunication can be an error of both the speaker and the listener, after all.