It is as much as if he had said, Lord! How should I believe on him, of whom I have not heard? (So the disciples answered Paul, asking them whether they had received the Holy Ghost, We have not so much as heard whether there be any Holy Ghost, Acts 19:2). But, saith he, Lord, I am ready to believe on him, may I but know who he is. Our Lord had prepared this poor man's heart for the receiving of him; there wanted now nothing but the due revelation of the Messiah unto him. This our Saviour giveth him.
Related Commentaries of John 9:36
John 9:36
36 He answered and said, Who is he, Lord, that I might believe on him?