I am standing before Caesar’s judgment-seat (Hestōs epi tou bēmatos Kaisaros eimi). Periphrastic present perfect indicative (hestōs eimi), second perfect participle hestōs of histōmi (intransitive). Paul means to say that he is a Roman citizen before a Roman tribunal. Festus was the representative of Caesar and had no right to hand him over to a Jewish tribunal. Festus recognized this by saying to Paul “wilt thou” (theleis).
Where I ought to be judged (hou me dei krinesthai). Rather, “Where I must be judged,” for dei expresses necessity (it is necessary). Paul exposes the conduct of Festus with merciless precision.
As thou also very well knowest (hōs kai su kallion epiginōskeis). “As thou also dost understand (hast additional knowledge, epiginōskeis) better” (than thou art willing to admit). That this is Paul’s meaning by the use of the comparative kallion (positive kalōs) is made plain by the confession of Festus to Agrippa in Act 25:18. Paul says that Festus knows that he has done no wrong to the Jews at all (ouden ēdikēka) and yet he is trying to turn him over to the wrath of the Jews in Jerusalem.