Passage
Then the disciples looked one on another, doubting of whom he spake.
Then the disciples looked one on another, doubting of whom he spake.
John 13:20 Verily, verily, I say unto you, He that receiveth whomsoever I send receiveth me; and he that receiveth me receiveth him that sent me.
John 13:21 When Jesus had thus said, he was troubled in spirit, and testified, and said, Verily, verily, I say unto you, that one of you shall betray me.
John 13:22 Then the disciples looked one on another, doubting of whom he spake.
John 13:23 Now there was leaning on Jesus’ bosom one of his disciples, whom Jesus loved.
John 13:24 Simon Peter therefore beckoned to him, that he should ask who it should be of whom he spake.
The verse centers on "disciples", "looked", "another", "doubting", and "spake". It is saying that the verse draws attention to "disciples" and "looked", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 21's "When Jesus had thus said he was..." into verse 23's "Now there was leaning on Jesus bosom...", so "disciples" and "looked" belong inside that flow. In John context, the local focus is the identity of Jesus, new birth, eternal life, and belief and unbelief.
A plain takeaway is to answer the verse's own emphasis on "disciples" and "looked" with trust shaped by these words, not by a vague optimism outside the passage.