If you have a bulky sporran, as mine usually is for causual attire, I remove it or slide it off to one side or even slightly to the rear.

If it is slim, as when my jacket or coat has enough pockets to allow for less things in the sporran, I leave it in front and put the apron over top.

When in formal attire, my present sporrans are slender and also deep enough that I also leave them on and put the apron on over top.

It really comes down to a judgement call, depending on appearance. It's always easy enough to remove the sporran and lay it on the floor or a seat beside you if it makes too much bulk under the apron.

I envy you seeing the ritual of the Fellowcraft degree for the first time. The staircase lecture is one of my favorites!