Exegesis:

kai apekrithēsan mē eidenai pothen lit. ‘and they answered not to know where,’ i.e. ‘that they did not know where it came from.’

Translation:

Whence it was, or, ‘who caused/sent/told him (to baptize),’ ‘from where its origin,’ cf. on v. 4.

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.