How to navigate spaces in a dual monitor setup?
Here's a shell one-liner that will do what you ask:

cliclick -r m:=-50,300 w:50 kd:ctrl kp:arrow-left ku:ctrl w:50



cliclick is a tool to move the mouse and is unfortunately necessary for this
-r: When done, move the mouse back to where it was when it started
m:=-50,300: move the mouse to the coordinates (-50, 300). The = is to actually do negative x values (for another monitor) rather than relative
w:50: wait 50 milliseconds
kd:ctrl: Press control key
kp:arrow-left: Press and release the left arrow
ku:ctrl: Release control key
w:50: wait 50 milliseconds


(0,0) is the upper left corner of the primary monitor.