The shower knob turns but no water comes out. And it does not have a "cover" on the handle itself, so there is nothing to pry off to remove a screw. I believe it is a Moen faucet. It has a smooth handle and I do not know how to find "access" to a screw to get it off. Does the whole knob spin somehow?

Can u post a picture?

Look under handle to see if it has a set screw there.

Chuck