¿En qué trabajas?
¿Cuál es tu profesión?
Both of them are used in normal contexts.
What you've been told is not, though. "Qué haces" is just "What do you do", which can be answered in multiple ways. If someone asked me "Qué haces" I wouldn't answer telling my job. "Qué trabajas tú" is ungrammatical, you shouldn't say that.