My keyboard didn't come with knobs, but with some carefully placed extra wires and some spare pins on the controller I added them.

I used them for PgUp/PgDown (to scroll up/down in a terminal), mouse wheel scroll, and cursor keys.

However, my hack job eventually caused problems. I think I had an intermittent short somewhere. I removed the knobs, and I don't miss them.

I may add a knob on a horizontal rather than vertical axis, but I should 3D print something to hold it in the correct place if I do this.