Senses
干什么/ 幹什麼 variants: 幹甚麼 to do what
To do what or do something; used to ask about an action or purpose.
干什么/ 幹什麼 no matter what
Used in constructions with 都 or 也 to mean "no matter what one does" or "whatever one does"
干什么/ 幹什麼 variants: 幹甚麼 why
Colloquial way to ask "why" or "for what reason", often expressing surprise or impatience.