"Ne, kio?"

Translation: No, what?

[no.name.42]

Is this a response to a question like: "Do you know what I did today?"?

[madam_im_adam]

So, if someone were to ask you a question and you didn't understand it, would you respond with "Kio?" like you would say "what?" in english? or is it like a few other languages where saying "how?" is more appropriate to say in non-informal situations

[FumuCxiuta]

People in the 50s used to say "How's that?" for "what".

[ZachTorino]

Could you use: "Pardonon?"