All things bear record · 2 Corinthians
4 witnesses of Christ here, and 1 further echo from the reading.
It is not expedient for me doubtless to glory. I will come to visions and revelations of the Lord. 2 Corinthians 12:1
Paul turns to the visions and revelations the Lord has given him. His witness rests on revelation from the Savior, not on human credentials.
Christ — the Anointed One
I knew a man in Christ above fourteen years ago, (whether in the body, I cannot tell; or whether out of the body, I cannot tell: God knoweth;) such an one caught up to the third heaven. 2 Corinthians 12:2
Paul humbly describes himself in the third person as "a man in Christ" who was caught up to the third heaven. Being "in Christ" is the heart of his identity.
How we know: the verse itself names Him
For this thing I besought the Lord thrice, that it might depart from me. 2 Corinthians 12:8–9
The Lord Jesus Christ answers Paul's prayer directly. He does not remove the thorn, but promises that His grace is enough and His power is shown most clearly through human weakness.
How we know: the verse itself names Him
Christ — the Anointed One
Therefore I take pleasure in infirmities, in reproaches, in necessities, in persecutions, in distresses for Christ’s sake: for when I am weak, then am I strong. 2 Corinthians 12:10
Paul welcomes hardship for Christ's sake because Christ's strength fills him when he is weak.
How we know: the verse itself names Him
Christ — the Anointed One
Again, think ye that we excuse ourselves unto you? we speak before God in Christ: but we do all things, dearly beloved, for your edifying. 2 Corinthians 12:19
Paul says everything he speaks is said in God's presence and in Christ, meaning as one united with the Savior and accountable to Him.
How we know: the verse itself names Him