Do you think that Wittgenstein knew he was a genius before people started
He did not seem initially to have thought that he was a genius at philosophy and required confirmation from colleagues before he was prepared to concentrate on it. On the other hand, he obviously had a pretty firm idea of his own talent at a variety of intellectual activities. He also had an income and a supportive family which made the pursuit of what interested him possible.
Your question is about the notion of the genius whom no-one appreciates in his or her lifetime, but who nonetheless has a strong sense of their genius.This must always be possible, since there are cases where an individual is the best judge of the work being created, perhaps it is so ahead of its time or out of sync with the culture out of which it emerged. On the other hand, it is worth the individual being aware of the likelihood of self-deception on this issue. It is all too easy to interpret not being very good at something as being a misunderstood genius. That is perhaps why Wittgenstein sought the advice and opinions of others before he felt it was worth concentrating on philosophy.