"I know it, but do you?"
Translation:Ja to wiem, ale czy ty to wiesz?
I’m not sure it should be accepted, the implied meaning is not really the same. With "I know it, but do you?" you are implying that the other does not know, whereas there is no such implied meaning in "I know it, and you?".
The "a" is more of a "but" than an "and" though, as in "to, a nie tamto" (this but not that).
I see what you mean though. It could also mean "and". I think it depends on intonation.
"A ty?" is the idiomatic way of saying "And what about you?", so I’m not sure it could mean "but", but maybe it depends indeed on the intonation.