So Simon Peter motioned to him to ask Jesus which one He was talking about.
Cross References
John 13:23One of His disciples, the one whom Jesus loved, was reclining at His side.
John 13:25Leaning back against Jesus, he asked, "Lord, who is it?"
Acts 21:40Having received permission, Paul stood on the steps and motioned to the crowd. A great hush came over the crowd, and he addressed them in Hebrew:
Treasury of Scripture
Simon Peter therefore beckoned to him, that he should ask who it should be of whom he spoke.
beckoned.
Luke 1:22
And when he came out, he could not speak unto them: and they perceived that he had seen a vision in the temple: for he beckoned unto them, and remained speechless.
Luke 5:7
And they beckoned unto their partners, which were in the other ship, that they should come and help them. And they came, and filled both the ships, so that they began to sink.
Acts 12:17
But he, beckoning unto them with the hand to hold their peace, declared unto them how the Lord had brought him out of the prison. And he said, Go shew these things unto James, and to the brethren. And he departed, and went into another place.