Give God the praise - This expression seems to be a form of administering an oath. It is used in Joshua 7:19, when Achan was put on his oath and entreated to confess his guilt. Joshua said, “My son, give, I pray thee, glory to the Lord God of Israel (in the Greek of the Septuagint, the very expression used in John, ‘Give God the praise’), and make confession unto him.” It is equivalent to an adjuration in the presence of God to acknowledge the truth; as the truth would be giving God praise, confessing the case before him, and trusting to his mercy. Compare 1 Samuel 6:5 The meaning here is not “give God praise for healing you,” for they were not willing to admit that he had been cured John 9:18, but confess that there is imposture in the case; that you have declared to us a falsehood, that you have endeavored to impose on us; and by thus confessing your sin, give praise and honor to God, who condemns all imposture and falsehood, and whom you will thus acknowledge to be right in your condemnation. To induce him to do this, they added that they knew, or were satisfied that Jesus was a sinner. As they considered that point settled, they urged him to confess that he had attempted to impose on them.
We know - We have settled that. He has broken the Sabbath, and that leaves no doubt.
A sinner - A violator of the law respecting the Sabbath, and an impostor. See John 9:16.