King James Bible
"Simon Peter therefore beckoned to him, that he should ask who it should be of whom he spake."
Peter signals to the disciple whom Jesus loved (likely John), who was reclining closest to Jesus at the Last Supper. This non-verbal communication reveals Peter's characteristic boldness coupled with indirect approach, using his position to gain information through an intermediary. Peter wants this disciple to inquire about the identity of the betrayer Jesus just mentioned. The request shows the disciples' confusion and urgent need to understand Jesus' cryptic announcement about betrayal. This refers back to Jesus' statement that one of them would betray him. The phrase emphasizes the gravity of the moment—the disciples are trying to comprehend that one among their inner circle will commit the ultimate act of disloyalty.