Rear Stud axle Weel Nut

For what reason?

I think that is "stub axle".

A pair of pliers should remove the cotter pin and the nut easily; it should not be very tight. Putting it back on will require the big socket tho. That requires torquing and backing off.

I think it is a 6-point nut on my car; doubt that has changed.

I had thought 30 mm for mine based on searching, but it was not. I did not note what the size was in the same place that I noted that it was not 30.

Are you trying to figure out if a cutting torch would be the tool of choice? Let's assume he is doing it for one of the normal reasons, and is not trying to be destructive.

99.5 and up use a sealed rear axle bearing. You can't take them off without making them useless as they are pressed onto the stub axle.

30mm, I think.