Since verse 20 already contains a reference to Peter’s seeing the other disciple, it may be necessary to mark this fact at the beginning of verse 21 by some transitional device, for example, “and so when Peter saw him.”

What about this man? (so also Revised Standard Version) is literally “but this man what?” Several translations render “what about him?” (Moffatt, Phillips, Jerusalem Bible, New American Bible), while New English Bible has “what will happen to him?” One may also render this question “what will this man experience?” or “what is he going to undergo?” or “how are people going to treat him?”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .