I have a 2004 CK30hst with the same knob. Open the hood and you'll see where the cable for the knob runs to the fuel shut off lever on the injection pump. This will be on the right side toward the front of the engine. The electric shut off solenoid will be just in front of where this cable connects. It must be caught on something there or maybe the cable froze. The cable isn't anything more than what you'd find on a lawn mower throttle. A steel wire in a wire spring like tube covered in black plastic. Once you take a look, you'll see the setup is pretty simple and you should be able to figure out the problem.
... In our years of tractors, the power is always off to the soleniod leaving the fuel shut off lever always on for fuel flow. The soleniod is only energized for about five seconds when you turn the key off which cuts off the fuel during these five seconds, stops the engine, and then you should here a click indicating the power is now off again to the solenoid and the fuel shut off lever is back to it's on position to allow fuel flow. I believe around 2008 or 2009, Kioti reversed this and power to the soleniod opens the fuel flow.....