Formal:
* আপনি কি করছেন? (Aapni ki korchhen?)
Informal:
* তুমি কি করছো? (Tumi ki korcho?)
Explanation:
* আপনি (Aapni) is the formal form of "you", used for showing respect.
* তুমি (Tumi) is the informal form of "you", used with friends or family.
* করছেন (korchhen) and করছো (korcho) are both forms of the verb "to do" conjugated for "you" in the present continuous tense.
Both phrases literally translate to "Are you doing what?", but in English, we use the more natural "What are you doing?".