John Gill Commentary John 9:29

"We know that God hath spoken unto Moses: but as for this man, we know not whence he is." — John 9:29 (ASV)

We know that God spoke to Moses
Out of the bush, and told him who he was, and sent him to deliver the children of Israel out of Egyptian bondage, and spoke the ten words, or law unto him, and by him delivered them to the children of Israel, and to whom he spoke face to face, as a man does to his friend, and mouth to mouth, and not in dark sayings; they mean, they knew that Moses had his mission, commission, and credentials from God:

but as for this fellow ;
so they contemptuously called the Lord Jesus Christ,

we know not from where he is ;
contradicting what others of them had said, (John 7:27) . They imagined they knew the country from where he came, which they supposed to be Galilee, and the place where he was born, which they concluded was Nazareth; though in both they were in the wrong; and they knew his parents, Joseph and Mary, and his brethren and sisters; but as to his divine filiation, they knew nothing of it; nor would they own his mission, commission, and credentials to be from heaven; and pretended they had no reason to conclude they were.