The phrase "Who shot Count Olaf?" is a play on the classic question "Who shot J.R.?" from the soap opera *Dallas*.
It's meant to be a humorous reference to the evil Count Olaf from the *A Series of Unfortunate Events* books (and Netflix series) who is always plotting against the Baudelaire orphans.
There is no real answer to the question as it's a joke. However, it's fun to imagine who could have been behind such a deed! 😉