A.T. Robertson Commentary John 9:36

"He answered and said, And who is he, Lord, that I may believe on him?" — John 9:36 (ASV)

And who is he, Lord, that I may believe on him? (Κα τις εστιν, κυριε; ). The initial κα (and) is common (Luke 10:29; Luke 18:26). Probably by κυριε he means only "Sir." It usually comes at the beginning of the sentence, not at the end as here and verse 38.

That I may believe on him (ινα πιστευσω εις αυτον). Ellipsis to be supplied before this final clause. He catches up the words of Jesus in the preceding verse, though he does not yet know who the Son of Man (or Son of God) is, but he trusts Jesus.