In short you can't display the Dock on multiple Spaces at the same time.
The Dock is only visible on one Space (i.e. display or screen) at a time. You can make the Dock move or appear on any Space by placing your mouse pointer at the bottom of the Space. The Dock will slide up from the bottom and remain on that Space until you move your mouse pointer to the bottom of another Space. You can enable a setting to "Hide and Show" the Dock, which will make the Dock slide up from the bottom of any Space when you place your mouse pointer at the bottom of the Space. Move the mouse pointer away from the Dock and it will slide down to be hidden.
I use the Dock with the "Hide and Show" setting enabled.