One working with Norma on hill? (8)
I believe the answer is:
Here is my best explanation:
'one working' is the definition.
'norma on hill?' is the subsidiary indication.
'norma' becomes 'opera' (norma is an opera by vincenzo bellini).
'on' is a charade indicator (letters next to each other).
'hill?' becomes 'tor' (tor is a kind of hill).
'with' is the link.
(Other definitions for operator that I've seen before include "Poor rate for a businessman", "Telephone controller", "Person who runs a machine or a business", "Switchboard worker", "Manipulator", "Switchboard employee", "Agent that runs some apparatus or machine", "agent", "Person working a switchboard" and "(Machine) user".)