Is this metal box grounded already?
Chicago doesn't have ground wires.  Everything in Chicago is in metal conduit with metal boxes.  Those, together, provide the grounding system for everything.
I mean, you're allowed to add ground wires if you really want to - belt and suspenders.
Every junction box should have a screw hole that is pre-tapped #10-32 for a ground screw. (you can also add them with a drill).   Sometimes installers accidentally use that hole for a mounting screw.  The ground screw is where you attach any &quot;belt and suspenders&quot; ground wires and any appliances with a ground pigtail.
Switches ground via the steel yoke and steel mounting screws.  Even though the yoke won't be landing hard on the steel box (since it's recessed into the wall), &quot;via the screw head&quot; is good enough for a switch.
Not for a receptacle. That needs clean-metal hard-bottomed-out contact between yoke, optional spacer, and box.  No rust, paint or those little squares that hold the screws on.
OR, a receptacle labeled &quot;Self-grounding&quot; can ground through the screws like a switch does.