This question shows a misunderstanding of the word "know" as used by Jesus in John 17:3. This misunderstanding and this question about it, gives the verse the appearance of saying something that it is not truly saying about who the true God is and who the source of eternal life is. Would Jesus say what he said if what he said is lacking and that "knowing God cannot give eternal life"? Is there any record of anybody asking or correcting Jesus that knowing God "alone" cannot give eternal life?
they may know
Verb - Present Subjunctive Active - 3rd Person Plural
Strong's 1097: A prolonged form of a primary verb; to 'know' in a great variety of applications and with many implications.
Know as defined above shows more than the OP's use of "knowing God alone". The kind of knowledge in John 17:3 is not the kind of knowledge that Adam and Eve had after eating the fruit of the tree in the midst of the garden. This knowledge made Adam and Eve behave according to their standards and placed their judgments above God instead of obeying God.
The needed knowledge is knowledge about God and His purposes. This kind of knowledge implies devotion to God and obedience to his Christ and this is implied in John 17:3. This is knowledge in a great variety of application and with many implications. We are however advised to be on guard against philosophies that are falsely called knowledge, 1Timothy 6:20.
1 Timothy 6:20 ASV
O Timothy, guard that which is committed unto thee, turning away from the profane babblings and oppositions of the knowledge which is falsely so called
OP asks What is the meaning of the Term "The only True God'?
Jesus said in his prayer to his Father/God And this is life eternal, that they should know thee the only true God, and him whom thou didst send, even Jesus Christ. What reason is there to believe that Jesus' God/Father is not the true God or that there is another one besides his Father/God? Would Jesus pray to his Father/God, the only true God, if his Father/God is not the only true God? How can Jesus be the faithful and true witness, (Revelation 3:14) if what he said is not true? What reasons are there to believe that he is the only true God whom he identifies as his Father? Jesus could not be the only true God as the Father is because that contradicts what he said in his prayer in John 17:3.
According to Jesus, his and his Father's testimonies equals 2 testimonies as John 8:17-18 shows, Jesus said that the testimony of two men is true I am he that beareth witness of myself and the Father that sent me beareth witness of me. Thus, Jesus cannot be the only true God as his God is and be counted as "one", the cardinal number 1, as John 8:17-18 show. The only true God is not a composition of multiple persons nor is the one (1) true God a compound unity of persons.
John 17:3 ASV
And this is life eternal, that they should know thee the only true God, and him whom thou didst send, even Jesus Christ
Revelation 3:14 ASV
And to the angel of the church in Laodicea write: These things saith the Amen, the faithful and true witness, the beginning of the creation of God:
John 8:17-18 ASV
Yea and in your law it is written, that the witness of two men is true I am he that beareth witness of myself, and the Father that sent me beareth witness of me.
Jesus also said in his prayer to his Father/God that the Father's word is truth John 17;17. So if Jesus words and the words of his God are truths, what reasons do we have in this case, to say knowing God alone cannot give eternal life? If our understanding of the word "know" is the same as Jesus Christ meant it, then that can give us eternal life just as Jesus said it in John 17:3. Philosophies that are falsely called knowledge leads to ideas that contradict inspired writings will not give us eternal life. Paul warned Timothy of this kind of knowledge, empty words of false teachers, who make a show of their learning and seek to influence the congregation. 1 Timothy 6:20
John 17:17 ASV
Sanctify them in the truth: thy word is truth.
Timothy 6:20 ASV
O Timothy, guard that which is committed unto thee, turning away from the profane babblings and oppositions of the knowledge which is falsely so called;
The source of eternal life is Jesus' Father/God. Romans 6:23; John 17:3; 1 John 5:11
Romans 6:23 ASV
For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord
1 John 5:11 ASV
And the witness is this, that God gave unto us eternal life, and this life is in his Son
OP asks, As the scripture seems to mean that knowing God alone cannot Give Eternal Life?
The last part of the OP's question is a speculation. If the kind of knowing that Jesus use in John 17:3 is lacking, he would not have said what he said in John 17:3
In addition, the apostles never believed and taught that Jesus is their God nor their ancestors God as Acts 3:13 show.
Acts 3:13 ASV
The God of Abraham, and of Isaac, and of Jacob, the God of our fathers, hath glorified his Servant Jesus; whom ye delivered up, and denied before the face of Pilate, when he had determined to release him.