I am working my way through Nicoliades' "The Natural Way to Draw." In section 14 he begins to ask the student to draw a model nude, and clothed, in the same pose. I can't find any online references aimed at this. Do you know of any?
The simplest way to tackle that task is to draw nude first. Then, add clothing as a new layer on a nude painting. That’s the way I was taught how to draw people. First, you draw lines that represent human posture. Make them anatomically correct. Add muscles and skin next. Use the same logic when drawing nude/dressed models. You can use https://create.vista.com/features/background-remover/ tool to copy nude models onto an empty background, print multiple copies, and practice drawing clothing.