When that day comes (literally “in that day”) refers to the time mentioned in verse 25.

Him (a reference to the Father) is not explicit in the Greek text, though Good News Translation and Die Bibel im heutigen Deutsch make it so.

For a discussion of in my name see comments at 14.13. Most translators apparently prefer to render the phrase literally, but Goodspeed has “you will ask as my followers” and Die Bibel im heutigen Deutsch “then you will ask by appealing to me.”

Two different verbs for ask are used in this verse: aiteō (you will ask him) and erōtaō (I will ask him). See the discussion of them in verse 23. In the context the petition specifically relates to deeper understanding. The implication is that prayer will be granted and this fact is stated explicitly in 14.13: I will do whatever you ask for in my name.

And I do not say that I will ask him on your behalf (Phillips “for I need make no promise to plead to the Father for you”) indicates that Jesus will not have to call the Father’s attention to the needs of the disciples, for they can pray to the Father directly through the help of the Spirit.

In some languages there are complications in the placement of the negative not in the sentence I do not say that I will ask him on your behalf. This might mean in some languages “I say that I will not ask him on your behalf.” Compare, for example, the English sentence “I don’t think he will go,” which is really equivalent to “I think he will not go.” It may therefore be necessary to translate this part of verse 26 “I will not need to ask him on your behalf” or “… ask him to help you.”

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 .