I recently saw this question asked on the Internet. This is how I would respond.
In my debates with Jehova Witnesses JWs), Evangelicals and other Non-Catholics, I don't try to prove anything definitively from Scripture.
1. The old saying is true, "for some, no proof is necessary. For others, no proof is ever enough."
2. They read Scripture differently than we do.
a. They read Scripture to discover their doctrines within. In fact, the JWs are famous for rewriting Scripture in order to write their doctrines into it.
b. Whereas, we know that New Testament Scripture is written based upon the pre-existing Traditions of Jesus Christ. That which Jesus Christ taught the Apostles is the basis of the New Testament. Thus, we go to the Church for our understanding of the Word of God, not to Scripture.
3. Remember, we do not believe in the false doctrine of Scripture Alone.
Having said that, I still engage them, but on our terms, not theirs.
First of all, I keep in mind that proof texting is a no-win plan. As many texts as you provide to back up Catholicism, they can provide texts, which they twist, to support their errors. So, it's a stalemate.
So, my game plan is like this. Let's take the Divinity of Christ, for example.
JW says, "Proskyneo means obeisance and that proves that no one worshipped Christ in the early Church".
Me, "Mm? Then why do all the Early Church Fathers, worship Christ? Let me give you a list."
Polycarp, who was taught by the Apostle, St. John, in his Letter to the Philippians, said:
Now may the God and Father of our Lord Jesus Christ, and the eternal high priest himself, the Son of God Jesus Christ, build you up in faith and truth...and to us with you, and to all those under heaven who will yet believe in our Lord and God Jesus Christ and in his Father who raised him from the dead.
Another disciple of St. John, Ignatius, said:
Ignatius, who is also Theophorus, unto her which hath been blessed in greatness through the plentitude of God the Father; which hath been foreordained before the ages to be for ever unto abiding and unchangeable glory, united and elect in a true passion, by the will of the Father and of Jesus Christ our God; even unto the church which is in Ephesus [of Asia], worthy of all felicitation: abundant greeting in Christ Jesus and in blameless joy.
Being as you are imitators of God, once you took on new life through the blood of God you completed perfectly the task so natural to you.
There is only one physician, who is both flesh and spirit, born and unborn, God in man, true life in death, both from Mary and from God, first subject to suffering and then beyond it, Jesus Christ our Lord.
You get the drift, right? Now, I can tell you how the discussion will go. They'll say, "Christianity went into apostasy at the time of Constantine"
And I say, "that's not true. Again, the Church Fathers prior to Constantine all teach the same things the Catholic Church teaches today. It's your church that teaches heresy, and your church is the new comer. Let's see what Scripture says about that:
Gal 1:8 New World Translation
6 I am amazed that you are so quickly turning away* from the One who called you with Christ’s undeserved kindness to another sort of good news.+ 7 Not that there is another good news; but there are certain ones who are causing you trouble+ and wanting to distort the good news about the Christ. 8 However, even if we or an angel out of heaven were to declare to you as good news something beyond the good news we declared to you, let him be accursed. 9 As we have said before, I now say again, Whoever is declaring to you as good news something beyond what you accepted, let him be accursed.
You, Jehovah's, are adding to the Teaching of the Church which came by Jesus Christ, something new which we do not accept.
And that's how I would respond.
I hope that helps.