John Gill Commentary Acts 21:33

"Then the chief captain came near, and laid hold on him, and commanded him to be bound with two chains; and inquired who he was, and what he had done." — Acts 21:33 (ASV)

Then the chief captain came near
To the place where the Jews were beating Paul:

and took him
the Arabic version adds, "from them"; he rescued him out of their hands, as he himself says, (Acts 23:27) .

And commanded him to be bound with two chains :
partly to appease the people, and partly to secure Paul; who, he supposed, had been guilty of some misdemeanour, which had occasioned this tumult; these two chains were put, one on one arm, and the other on the other arm; and were fastened to two soldiers, who walked by him, having hold on those chains, the one on his right hand, and the other on his left; and thus Agabus's prophecy in (Acts 21:11) was fulfilled:

and demanded who he was ;
or asked and inquired about him, who he was, of what nation he was, what was his character, business, and employment: this inquiry was made, either of the apostle himself, or of the people; and so the Arabic version renders it, "he inquired of them who he was"; also

and what he had done ;
what crime he had been guilty of, that they used him in such a manner.