The only "one" who needs to know is God. I think He's capable of having that knowledge, don't you? But hey, thanks for the condescension and insult.
The point, however, is that by insinuating that there are people who only think they are born again means that we make different classes of Christians: there's a special class of Christians are "truly" born again, and there are those who aren't. And if we cannot know if we are born again, then we cannot know if we belong to God, and thus salvation inevitably is reduced to terrifying guesswork or trying to feel the right feels, think the right thoughts, or performing the right acts.
In distinction to this, however, Scripture tells us what the new birth is and where it is found, Jesus Himself tells us in John 3:5, that the new birth is to be born of "water and Spirit", which Paul echoes in Titus 3:5 when he says that not by works of righteousness which we have done, but by the "washing of regeneration, and renewal of the Holy Spirit".
All who are baptized into Christ have put on Christ. We can look to our baptism with absolute confidence that here, in these blessed waters, God has clothed us with Jesus Christ and all His righteousness, that we are born of God, anew, as a new creation, as an adopted child of God, and all other ways Scripture speaks of this truth.
We don't look to ourselves, or inside of ourselves, to find out whether or not we belong to God--because inside ourselves is only a pile of dead man's bones, the law of sin working itself through our mortal members. We can, therefore, look only outside of ourselves: to the Christ who suffered, bled, and died on the cross, who descended into death, and rose from the dead on the third day; and this Christ and His work is made ours, as pure gift, from God, through the works of God in Word and Sacrament. That it is through this Gospel of what Christ has done that God takes hold of us--sinful wretches that we are--and makes us Christ's, and if we belong to Christ, then we belong to God. And, therefore, we are children of God, heirs of God, joint-heirs with Jesus. And here we have life-giving hope, hope in this life that we belong to God, and hope for the next when we are raised up to that life everlasting in the age to come.
We must recognize the location of our salvation as outside of ourselves, in Jesus Christ and the gifts of God's grace through the Gospel by which we receive Jesus Christ and He us. For "it is not of yourselves, it is the gift of God" (Ephesians 2:8).
-CryptoLutheran