1 John 5:20
1 John 5:2020And we know that the Son of God has come and has given us understanding, so that we may know Him who is true; and we are in Him who is true—in His Son Jesus Christ. He is the true God and eternal life.
The 15 October 2004 Watchtower article "Who Is 'the True God and Eternal Life'?" defends the Father-reading of the closing sentence "This is the true God and life everlasting." The argument has the pronoun "this" (οὗτος) skip over its immediate antecedent — Jesus Christ — and reach back to "the true one" earlier in the verse (which on the Watchtower reading is the Father). That way the sentence ends with a statement about the Father, not a statement that Jesus is the true God. The NWT keeps the sentence in the text without footnote.
The grammatical question is what "this" refers to. The immediate antecedent in the Greek sentence is "Jesus Christ." Murray Harris in Jesus as God (Baker) — along with the majority of modern critical grammarians — reads 5:20 as a Christological climax, an inclusio that bookends the Johannine corpus alongside and Thomas's confession in ("My Lord and my God"). The Watchtower can make its case, but only by overriding the standard immediate-antecedent rule, and the NWT does not footnote the sentence out. You do not need to win the grammar debate at the door. The point is simpler: the NWT's own text ends 1 John with "this is the true God and life everlasting," and — the verse the rs book uses to define antichrist — flags whoever denies the Son. Ask whether the Watchtower affirms that Jesus is the true God or denies it; on its own answer, the rs antichrist boomerang comes home. Present the Christological reading as "the most natural and the majority critical view" — not as something your JW friend must concede this minute.
Not a translation-wording divergence — NWT renders the Greek faithfully enough to keep the sentence intact, including the closing clause "this is the true God and life everlasting." The "issue" is interpretive: the 15 October 2004 Watchtower article defends the Father-reading of "this" by having the pronoun skip its nearest antecedent (Jesus Christ), an override of the standard grammatical rule. The divergence is at the level of the Watchtower's explanatory note, not the rendering itself.