Jesus turned, and saw them following, and said to them, "What are you looking for?" They said to him, "Rabbi" (which is to say, being interpreted, Teacher), "where are you staying?"

 John says that he did not know Jesus. Now John was a relation of Jesus ( Luke 1:36), and he must have been acquainted with him. What John is saying is not that he did not know who Jesus was, but that he did not know what Jesus was. It had suddenly been revealed to him that Jesus was none other than the Son of God. 