Most likely the questioning and the subsequent events took place on the day after the healing. This is clear from two circumstances. The blind man is led to the Pharisees and set before the assembly (v. 14), which could not have taken place in the ordinary course of things on the Sabbath. Also, from verses 7 and 12 we see that the man who received sight either did not return to the Lord, or more likely did not find Him if he came to thank Him.
For to the question, "Where is He?" the man who received sight answers, "I do not know." From this one must conclude that on the Sabbath, the day of his receiving sight, he did not see the Lord. Otherwise, of course, he would have recognized Him in the temple when the Lord Himself found him (v. 35).
The whole narrative about how the man born blind sat and begged, how his neighbors questioned him, how they led him to the Pharisees, and the answers of the man who received sight before the assembly, was clearly written by an eyewitness of the events. This witness received all these details partly from the healed man's own mouth, and partly by personally seeing and hearing everything.
This eyewitness of the events was, of course, the Evangelist John. In all probability he himself spoke with the man who received sight after our Lord found him in the temple, and after he worshiped the Lord and confessed Him to be the Christ (v. 38).
It must be added that the neighbors probably led the man who received sight not to the supreme tribunal, the Sanhedrin, but to the synagogue. Apart from its meaning as a religious assembly, the synagogue was also clothed with a certain judicial authority concerning violations of religious rites and ordinances.
Below, this same synagogue decides to expel the man who received sight, that is, to excommunicate him. Compare verse 34 of this chapter with verse 22 of the same chapter, and below, Jn 12:42.