Albert Barnes on John 16:8

He will reprove. The word translated reprove means commonly to demonstrate by argument, to prove, to persuade anyone to do a thing by presenting reasons, It hence means also to convince of anything, and particularly to convince of crime. This is its meaning here. He will convince or convict the world of sin. That is, he will so apply the truths of God to men's own minds as to convince them by fair and sufficient arguments that they are sinners, and cause them to feel this. This is the nature of conviction always.

The world. Sinners. The men of the world. All men are by nature sinners, and the term the world may be applied to them all, Jn 1:10, 12:31, 1Jn 5:19.

(1) "reprove" or, "convince" Acts 2:37