Question: System Settings can be run from the launcher (pinned by default), the Dash, or the power cog. But what command would I enter in a terminal window if I want to run it from there?

Answer: 
if you run `gnome-control-center` and get `command not found`, you can install it with:

```
sudo apt install gnome-control-center

```
I found a different solution...

1. I tried removing/installing `gnome-control-center`; this did reinstall the application I still couldn't open it.
2. Later I found that it would start up on the side of the screen and I couldn't access it
3. I changed the display mode to single display and it came back. Hope it helps.