The man answered is literally “that one answered and said.” In Greek Tell me who he is, sir is literally “And who is he, sir…?” (Revised Standard Version) New English Bible translates exactly as Good News Translation does, and Jerusalem Bible is similar, “ ‘Sir,’ the man replied ‘tell me who he is….’ ” Sir in this verse is the same as the word translated Lord in verse 38. But most translators and commentators see a development from verse 36 to verse 38. In verse 36 the man merely addresses Jesus with a polite form of address, but in verse 38 he confesses that Jesus truly is Lord.

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .