How to tell if light switch box is grounded
You have metal conduit connecting metal junction boxes.

All of it is ground.  The conduit, the boxes, all of it.  This is the ideal system.  

Switches ground through the yokes and mounting screws. They don't need ground wires.

Receptacles are not allowed to do that unless they yoke has hard clean flush metal-metal contact with the box, and yours won't because the box is painted.  However, in the back of the junction box will be a hole that is tapped #10-32 for a ground screw.  Any #10-32 screw will do, but they sell little green ones very cheap.  Then you can just run a recep ground to the green screw.