I have two monitors, but only one dock, which is somewhat annoying, so my question is, how do I get multiple docks? (One on each screen)
There is no way of doing that.
When the Dock is configured to appear at the bottom of your screen, it's available on whichever screen you’re working on. Just move your pointer to the bottom of either display. When the Dock is configured for the left or right position, it appears on the leftmost or rightmost display edge.
Tip: If you don't see your dock because it's set to hidden or there's a full screen app on the display, move your pointer to the location of the Dock. If the Dock still doesn't appear, swipe your pointer towards the Dock again to unhide it.
I had Dock on all monitors, but suddenly it stopped working. I found out that Dock on all monitors only works if Mission Control -> Displays have separate Spaces is checked. I'm using Mojave 10.14.
Displays have separate Spaces:
- CHECKED Dock appears on all monitors, but you can't span a window across multiple monitors.
- UNCHECKED Dock does not appear on all monitors, but you can span a window across multiple monitors.