Can gnome display two workspaces at the same time? I have two monitors, and I want to display a workspace on one monitor and another workspace on the other monitor. I think this way of working will be very efficient.
Not with standard GNOME.
If you look in the multitasking page of the control center, you can find an option on how to deal with multiple monitors.
They can either show a static workspace (should be the default), or extend the workspace of the primary window and be switched with it.
What you describe may be interesting regarding its flexibility, but the question is: How would you control it. You would need to find a design in which you can, intuitively, switch workspaces monitor-independently, move them across monitors, and show this in the overview.
I think for standard GNOME this is too complex to be considered. Might make a good extension though.