I'm wiring in a light switch and light into a closet on the other side of the wall of this outlet. I've run romex from the lightswitch hole through the wall and into the back of this metal box (secured with a clamp). The metal box receives power from some flexible metal conduit with a black and a white wire in it. I've attached the white and black wires from the romex to the open screws on the outlet. Now I'm wondering what the proper way to wire the ground is.
In the picture, you can see that the prior wiring had a small wire connecting the ground screw on the outlet to the neutral screw coming out of the wall. Perhaps the previous electrician used this to retrofit the old two prong outlet to a three prong one. The box doesn't have an obvious ground spot. Besides my new romex, there are no other wires.
The house was built in 1923 in Minnesota and has had various renovations over the years. The prior owner owned the house since 1947 and almost always had professionals do the work. The wall is plaster/lathe.
I added some more photos of the old wiring. I found a spot in the box where it seems like I can thread a bolt, I'll try grounding it there.