Yes, I think it may be a view port to a Sherman. However, I am no expert... so wait for others to respond.
I would agree , i think it's part of a sight for a Sherman tank ...
I thought the viewing port on the turret was oval shaped ? Maybe a drivers view port.
looks very much like the top section of the periscope fitted to the shermans and some others
spotter is right it's the top part of an m6 periscope used in the sherman.