John Gill Commentary John 8:16

"Yea and if I judge, my judgment is true; for I am not alone, but I and the Father that sent me." — John 8:16 (ASV)

And yet if I judge, my judgment is true
Because he saw not as man did, nor looked unto, and judged according to the outward appearance of things; but looked into the heart, and knew what was in it, being the searcher and trier of it; to whom all things are naked and open, and therefore cannot be deceived or imposed upon; his judgment must be sure and infallible:

for I am not alone, but I and the Father that sent me ;
he was not separate from the Father, or at a distance from him, when he was here on earth; he was in his bosom, and in heaven, as the Son of God, when as the son of man, he was below; nor was he alone in his testimony and judgment, the Father joined with him therein: and which is a further proof of the truth of his testimony, and the certainty of his judgment.