To remove the knob, just drive it out.
There is a flare at the bottom that
will collapse. You will need reposition
the flare when you put it back in. You
probably can only get by doing this once.
If you want to disassemble the knob
to make replacement parts it has a
countersunk hole in its top.
The top end of the pin is flattened,
to hold it together and smoothed off.
The slot in bottom would lead one to
believe it’s a screw, but it’s not.
Tubs.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.