How to mirror an application window in a second display?
You can use an application like tmux within which you can run your first terminal session (on first display), and then open a different terminal window on the second display and use tmux attach-session to mirror the session that is already running on the first display. This should allow you to run and view commands from both the displays.

Note that this technique is only useful for mirroring the terminal and no other GUI program.