A.T. Robertson Commentary John 13:26

"Jesus therefore answereth, He it is, for whom I shall dip the sop, and give it him. So when he had dipped the sop, he taketh and giveth it to Judas, [the son] of Simon Iscariot." — John 13:26 (ASV)

He (εκεινος). Emphatic pronoun again.

For whom I shall dip the sop (ω εγω βαψω το ψωμιον). Dative case of the relative (ω) and future active of βαπτω, to dip (Luke 16:24). Ψωμιον is a diminutive of ψωμος, a morsel, a common Koine word (in the papyri often), in N.T. only in this passage. It was and is in the orient a token of intimacy to allow a guest to dip his bread in the common dish (cf. Ruth 2:14). So Mr 14:20. Even Judas had asked: "Is it I?" (Matthew 26:22).

Giveth it to Judas (διδωσιν Ιουδα). Unobserved by the others in spite of Christ's express language, because "it was so usual a courtesy" (Bernard), "the last appeal to Judas' better feeling" (Dods). Judas now knew that Jesus knew his plot.