I really don’t recall seeing enough to tell me where the cane was landing any more than my own eye watching it land. A good caning will leave marks but the immediately visible marks weren’t really that noticeable. Honestly, I don’t think most teachers new to caning are going to be accurate enough that knowing exactly where a stroke landed matters much. The seat of a boy’s trousers is a surprisingly small area. Precise placement takes a lot of practice.
I’ve had a teacher ask to observe a few canings when they became authorized to use the cane so they could get some idea of precisely what they were supposed to be doing, but it’s hardly rocket science. Really, you just have to know how not to cause unintended effects for reasons of safety, but once you do that, I think it’s learning as you go. The first few boys I caned, I know I could have done a better job but I didn’t injure them and I made it unpleasant enough for it to work and that is what mattered.