"What are you doing?" is the Engpsh way of asking "在干嘛?" in Chinese. This phrase is a common question used to inquire about someone's current activity or occupation.
Its origin can be traced back to Middle Engpsh, where "do" was used as a verb meaning "to perform" or "to undertake". The phrase became widely used as a popte way to ask someone what they were up to.
Examples:
What are you doing today?
(今天在干嘛?)
What are you up to this weekend?
(这个周末在干嘛?)
What are you working on?
(在做什么工作?)