Nelson,
On a lot of earlier machines, it is screwed in from the underside of the tailstock nose, so have a close look underneath (the screwhead might just have been filled up with paint).
On later machines, it is sometimes dropped into the slot deepened with a drilled hole, and can usually be lifted out with a pair of long nosed pliers, failing that, use a small chisel (I didn't tell you to use an old screwdriver) and tap the nearest edge to you in an upwards direction. That usually gets them out, but you might need to dress it clean afterwards, so that you can put it back in.
That pin is in there to stop the tailstock ram from rotating as it is screwed in and out, so isn't a bit that can be discarded, but I have made new ones to stop the ram from rotating a little too much when this pin gets worn over time.
I hope this helps
John