It looks like a Guard Top - single-function switch. Since it is located in proximity to the Winch, it would be my SWAG that it is for the winch.
As it is on the deck, there should be a breaker for the winch located in the cabin to power it. If you switch on the breaker with DC power and it still does not cause anything to function, then you will need to explore the DC Power availability, the wiring, and connections for the winch and the switch.
Oh, the fun we have when buying a new-to-us boat.