Here's the answer:
“你做什么的?”
(nǐ zuò shén-me de?)
Watch a real native speaker say it:
Here's how it sounds in a textbook:
Fun fact: the hundreds of thousands of people learning Chinese with Memrise get this phrase correct 86.93% of the time!
(nǐ zuò shén-me de?)
Fun fact: the hundreds of thousands of people learning Chinese with Memrise get this phrase correct 86.93% of the time!