The knurled knob is confusing, but I read on the PDF sheet that it has Morris 2 tapers.
The metal rod that pushes out spurs is called a knockout bar. I needed a longer one for my lathe, so I tried a wood dowel. It worked, kinda, but felt spongy. I got a longer steel rod, and it works much better.
I suspect that the spur has been there for a while, and is stuck very well. I suspect that it is a Morris 2 taper (MT2) spur. I believe that at some point, you will want a steel rod to use as a knockout bar.
I do not understand the knurled knob. I wonder whether it is there to "lock" the spur in place so that it won't fall on someone's toe if it accidentally comes out.
If it were my lathe, I would do the following:
1. Loosen the knurled knob as far as it will go.
2. Use a tool (pliers?) to try turning the knurled knob a little further to see if it pops out the spur. If it gets tight, stop.
3. Use a vacuum to suck out whatever might be inside, behind the spur. Try taping a piece of aquarium hose to the end of your vacuum hose and insert the aquarium hose in the knockout hole.
4. Find a long steel rod that will fit inside the knockout hole. Give it a bonk with a hammer. What happens? Does the spur move at all? Does it bump against the knurled knob? Can you release it the rest of the way?
5. If the spur doesn't move at all, then try giving it some more very firm bonks to see if you can get it to move. What happens?
6. Try the knob again. What happens?
... 10. LAST RESORT: See if you can get some penetrating oil (liquid wrench) into the taper to help release the spur. This is a very BAD idea for many reasons, including the fact that you don't want to lubricate the taper, but maybe there is no other choice. Hopefully others will suggest better ideas.
You may want to think about what happens when the spur pops out. The point is sharp.