I have been asked a question I can’t answer. How and when did Paul know that he was the apostle to the Gentiles? Of course, you’ll back it up with scripture references.
In his letter to the Galatians, Paul identified himself as an Apostle, sent not from men nor by man, but by Jesus Christ and God the Father, who raised Him from the dead (Gal. 1:1). In Gal 1:11-24
Paul explained that after his conversion on the Damascus Road, he went into Arabia (probably Mt. Sinai) where he received the gospel message by direct revelation from the Lord so he could preach among the gentiles. During that time he was also taken to the throne of God to see things he was not permitted to describe (2 Cor. 12:1-4). According to Gal. 2:1 these things all happened over a period of time beginning 14 years before his trip to the Council at Jerusalem, which took place about 50 AD. Piecing this together, it appears that Paul would have known he was being called as an Apostle to the Gentiles sometime between 36-39 AD.