We know that God spoke to Moses, but as for this fellow, we don’t even know where he comes from.”
Some of the people knew of what they thought to be the origins of Jesus (John 7:27) but none of the Pharisees knew from where Jesus came (John 8:14). They regard their lack of knowledge of “where he comes from” to hurt the cause of Jesus, but in fact (also from John 7:27) no one will know from where the Messiah will come when He does. Morris states that if they had considered the implications of their argument they may have been led to the truth.
John 7:27 But we know where this man is from; when the Christ comes, no-one will know where he is from.”
John 8:14 Jesus answered, “Even if I testify on my own behalf, my testimony is valid, for I know where I came from and where I am going. But you have no idea where I come from or where I am going.