Exegesis:

oude egō legō humin ‘nor do I tell you,’ or, ‘then I too do not tell you,’ implying that Jesus, just as his opponents, refuses to answer their question.

Translation:

By what authority I do these things, cf. on v. 2.

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.