Is it "one of the registered nurse" or "one of the registered nurses"? (In spoken English)
Welcome to the forum.
In general, we always ask users to give us a complete sentence. However in the case of this fragment, there is a simple answer - only the second is correct. Whenever you use "one of the", it will be followed by a plural noun. That's because using "one of the" makes it clear that there is more than one of something.
Don't leave a space before a question mark.
Why did you specify spoken English? Do you think, for some reason, that the answer would be different for written English?