This is another text that a lot of people object too.
It reads in the NWT
"This means everlasting life, their taking in knowledge of you,
the only true God, and of the one whom you sent forth,
Other translations that appear to be more popular in the English language do not use the phrase "taking in knowledge". Instead they say "that they may (or should) know thee" RSV, KJV, ASV. "by knowing you" The Living Bible. "to know you" The Revised Berkeley Version. "that they may know you" NIV.
On reading these translation, the reader gets to fell that salvation comes from just knowing God and his Son, that is alll they have to do is have a knowledge of God. Whereas the NWT we are told that it is an ongoing process, continuing gaining knowledge. This indicates more is involved than just knowing about God but a continual commitment in getting to know God.
The word in question know or knowledge, centres around the Greek word "GINOSKO" GINOSKO.
Vines Expository Dictionary of New Testament Words says
VINE'S NEW TESTAMENT WORD SEARCH -COMPLETE
Know, Known, Knowledge, Unknown
A-1, ginosko, [Verb, 1097]
A-2, oida, [Verb, 1492]
A-3, epiginosko, [Verb, 1921]
A-4, proginosko, [Verb, 4267]
A-5, epistamai, [Verb, 1987]
A-6, sunoida, [Verb, 4923]
A-7, agnoeo, [Verb, 50]
A-8, gnorizo, [Verb, 1107]
B-1, gnostos, [Adjective, 1110]
B-2, phaneros, [Adjective, 5318]
B-3, epistemon, [Adjective, 1990]
B-4, agnostos, [Adjective, 57]
C-1, gnosis, [Noun, 1108]
C-2, epignosis, [Noun, 1922]
C-3, agnosia, [Noun, 56]
"GINOSKO … signifies to be taking in knowledge, to come to know, understand, or to understand completely"
A Manual Greek Lexicon of the New Testament by G. Abbott-Smith says "to be taking in knowledge, come to know, recognise, perceive, understand…. Of the knowledge of divine things, of God and Christ… Jo 17:3
The Greek word verb GINOSKO denotes the act of knowing through experience. Getting to know our Creator and his Son is always ongoing, just as it takes a lifetime to get to really know a close friend or relative. And the only way that we can really get to know our God is by regular and consistent study of his word.