I would be interested in the little known things about perspective. I have poured over perspective books trying to find answers for weird situations or at least what I think are weird. Maybe they follow normal rules but I can’t figure out how. One, for example that I kept wondering about was the vanishing points of something falling from the sky which will not be parallel to the ground plane.
I’d also be interested in your sketch book approach. I love looking at artists’ sketchbooks and seeing their process.