οὐ γὰρ ἐμὸν ἐρῶ τὸν λόγον ὃν ἂν λέγω, ἀλλ᾽ εἰς ἀξιόχρεων ὑμῖν τὸν λέγοντα ἀνοίσ
P.A. 20e

I cannot figure out why in the relative clause "ὃν ἂν λέγω" Plato uses "an" with the subjunctive. Smyth says that the subjunctive with "an" in ordinary relative clauses "expresses a possible or supposed fact in future time or a generality in present time." None of these seem to fit, and all of the translations I have seen translate the clause as "...which I am about to say." What is the signification of "an" with the subjunctive here?

διασκοπῶν οὖν τοῦτον—ὀνόματι γὰρ οὐδὲν δέομαι λέγειν, ἦν δέ τις τῶν πολιτικῶν πρὸς ὃν ἐγὼ σκοπῶν τοιοῦτόν τι ἔπαθον, ὦ ἄνδρες Ἀθηναῖοι, καὶ διαλεγόμενος αὐτῷ
P.A. 21c

Just a quick question. Is "onomati" considered a dative of respect,i.e. "...to say nothing with respect to his name"?

"Whatever I might say, is not mine", would be a correct translation of your text. Smyth explains the use of ἄν. To your second question. Ὀνόματι is a dative of respect, if by respect you mean not honour but simply reference.