Nespíš máte na mysli: "What are you up to?". Volně přeloženo: Co máš za lubem?

Kolegyně Aneta měla na mysli "What are you GOING to do." :-)

Hello, it's actually "What are you up to?" which can be used between friends, family members and colleagues to express:
or "What's happening?"
or "What are you doing (right now)?"
or "What have you been doing (up to now)?"
or "What are you busy with?"
or "What are you planning?"
or "Co (právě) děláš?"

In parent-child situations or in any context in which mischief may be afoot, the question communicates suspicion and is the equivalent of:
"Co máš za lubem?" and might be followed by:
"Hned mi řekneš, co máš za lubem, nebo ti nařežu na holou!"
This is quite different to the first meaning.