To see all your gcloud projects you use command gcloud projects list. To switch to a specific project, you use gcloud config set project PROJECT_ID.
But what command can you use when you want to check which project is active? By which I mean, on which project was called the set command last?
gcloud config get-value project
You can always type gcloud config --help
There's a very cool and well-hidden interactive tool: gcloud beta interactive that will help with gcloud command completion.
Personally, I recommend not using configurations to hold default values (for e.g. project) in order to (help) avoid "To which project did I just apply that command?" issues.
IMO, it's much better to be more explicit and I prefer:
gcloud ... --project=${PROJECT}
If, like me, you put the project value in a variable, you can still make mistakes but it is easier to avoid them.
You can also define sets of configurations and then use gcloud ... --configuration=${CONFIG} and this works too as long as you don't set values in the default config