Do nuns give bare-bottomed spankings to naughty girls?
Well, probably not, these days. But (a) it seems they may have used to, and (b) anything is possible in the movies. Hence, this screen capture, from a spanking clip called Catholics Corrected:
"...the girls are prepared in the reformatory’s punishment room, naked, lying on their backs on special benches, bound with their legs spread above their heads, shamefully showing the two holes usually hidden..."