I believe this form of sarcasm is not restricted to English speakers.
Therefore, it is not so much as what the phrase or word means in English but what it means in a social and relationship context. Rather, what do people mean to tell you, in whatever language you are conversing.
Are we going to school today?
Jessica, cutely gesturing with knuckles knocking on air next to Henry's forehead:
Hello, knock, knock, any body in there? Today is Saturday, dumbo!
Henry: Are we studying together tonight?
Jessica, shaking her head and up in arms in disbelief, after Henry had broken off with her last night, looking straight at his eyes:
We could simply explain that the person who is telling you "Hello?" is questioning
- if you are paying attention to reality of the present situation.
- if you have any common sense still intact
- if you had any intelligence
- if you are still alive in there
- if you are still human
- wtf were you thinking?
But explaining it in words what the verbal gesture means would be inadequate and not do it justice. The possibilities are many, but the sarcasm is obvious, in any language.