John Gill Commentary Acts 25:10

"But Paul said, I am standing before Caesar`s judgment-seat, where I ought to be judged: to the Jews have I done no wrong, as thou also very well knowest." — Acts 25:10 (ASV)

Then said Paul, I stand at Caesar's judgment seat
Not that here was a seat in the judgment hall built by Herod for Caesar himself to sit in, should he ever come there, as some have thought; but the seat on which Festus sat is called Caesar's judgment seat, because it was in a Roman court of judicature, and because Festus, who filled it, represented Caesar himself:

where I ought to be judged :
being a Roman citizen, and not at Jerusalem by the sanhedrim of the Jews, who had nothing to do with him:

to the Jews have I done no wrong, as you very well know ;
it may be by his predecessor Felix, who had informed him of this case; or by Lysias's letter, which might come to his hands; or by the apostle's answer and vindication of himself, which he now made.