Plumbing – Pedestal Sink Base Removal

The stud you would use a hole bit that is the same size as your piping to cut a circular hole. You can pick up these bits at big box or a place like Harbor Freight in the US.

You do need to make sure that the stud is not load bearing! If it is or could be we need more info and pictures.

It really looks like you have PVC but we can't see everything. If you need to go from PVC to cast iron use a coupling.

Tap (don't overdo it and break the "ears") with a hammer and nail or hammer and punch against the projecting "ears" - and do as many of them as you can easily reach, rather than only tapping on the most accessible one (at least until the thing starts to move.)

Scribe a line before you start that goes across both parts so you can detect even a small movement. The shock of tapping may start to move things where grabbing with pliers won't budge it.

If no joy, add heat - use a serious heat gun if you have one, or a torch VERY carefully and pretty much so far out that the flame isn't directly contacting the sink parts, at least at first.