Simon Peter motioned to this disciple and said, “Ask him which one he means.”
They were all looking in surprise at each other with their mouths hanging open. This is the moment represented in Leonardo da Vinci’s “Last Supper” although they were undoubtedly seated around the table on not just on one side.
Peter is sitting close enough to John that his motioning and words are apparently not picked up by the others, but not close enough to whisper to him, so he is probably sitting directly across from John.