Good question and you can go online and see pics of what they see - basically not too much. It’s not like X-ray vision where you can see me wearing my tight little thong under my clothes or something like that. Think its pretty boring and even worse with the population (broadly speaking) getting more and more out of shape, I’m not sure i’d like a job where i saw peoples’ shapes all day...
Similar to the actua X-ray machine, you can’t see someone’s underwear collection in their bags...they’ll only see that if they do a bag inspection. I’ve had that happen a couple of times!