Move dock between displays keyboard shortcut (or keep on both displays)
I thought perhaps the default [Opt + Cmd +D] to toggle Turn Dock Hiding On/Off would work. I considered that, depending on which display was active, that toggling the dock would cause it to appear on whichever display was active at the time. However, I find that dock remains on the given display.

However, I believe the solution is simply to explain how the mouse or trackpad is used to move the dock.

The rule is that by moving the cursor 1" below the bottom of the given display, the dock will then move.