prep for bathroom wall painting
It looks like patches to the sheetrock or maybe wet spots and the rock is not in good shape. You should evaluate if the sheetrock is not solid it should be cut out and replaced.
I usually use green board for repairs in bathrooms.(Green board is water resistant sheetrock). I would scrape and see if the paint is well bonded if it is well bonded fill the low spots with topping mud then prime for best results.