Qual è la differenza tra Who works on the fourteenth floor? e Who does work on the fourteenth floor？ ?Sentiti libero di rispondere con un esempio.

In general, when who is the subject of a sentence, you don't need to modify the verb in any way.

E.g. Salli0201 works on the fourteenth floor -> Who works on the fourteenth floor?

But if it isn't the subject, then the verb changes:
Salli0201 works for X company -> Who does Salli0201 work for?

In your particular question, however, both are valid, but they have a very different nuance. In the second question, work becomes a noun. "To do work" is typically used when talking of a short-term job/assignment/gig. So in the first question, you are asking for whom the 14th floor is the place where they work in general. In the second question, you're asking who is there to do a defined task and then leave.