"What needs must"?

Your question is not clear.

"needs" followed by "must" can only happen when "needs" is a noun. 'Their needs must be met.'

Could you post the whole sentence?

There is an expression "needs must", meaning that necessity forces one to do something that one might not otherwise be keen to do. I am not aware of any expression "what needs must".

RaenHow does the grammar work here?

Forget the grammar. This is a fixed expression from centuries ago, that is, at a time when it was grammatical. "needs must" or "must needs" just means "must", "have to", "has to".

http://www.phrases.org.uk/meanings/needs-mu

CalifJimThis is a fixed expression from centuries ago, that is, at a time when it was grammatical. "needs must" or "must needs" just means "must", "have to", "has to".

Does anyone still say that? I don't recall 'hearing' it currently and wouldn't recommend it to students.

canadian45Does anyone still say that?

Not that I know of. I've seen it in writing on a rare occasion, but I don't believe I've ever heard anyone use it in a conversation.

CJ

Thanks for the replies. They helped a lot and no, I never intended to use it at any time. I read that off of a page of a novel, British published. (Could that be why?) It confused me (and that was the whole sentence, by the way), that's why I asked. Thank you again.

Raenthat was the whole sentence

Then, depending on context, it means:

Whatever you have to do.
Do whatever has to be done.
A person does whatever a person has to do.

Or something similar.

CJ