What Is The Bible Verse That Says, "The Punishment Of Sin Is Death"?

The verse is in Romans chapter 6 verse 23 and says:
"The wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord."

The part quoted in the question emphasizes the negative aspect of the situation, whereas the whole verse is beautifully balanced.

In his epistle to the Romans, the Apostle Paul is systematically setting out his understanding of the message of the gospel. He has already shown that all people in the world are sinners:

"All have sinned and fall short of the glory of God" (Romans 3:23).

But then he goes on to describe what God has done to deal with the problem: he sent his son Jesus Christ to die in the place of sinner.

The verse in question, then, summarises the argument so far. We are all sinners and in sinning we have "earned" the punishment of death.
BUTGod offers as a free gift, eternal life.Ho can he offer this? Because Christ Jesus out Lord died instead of us and now by trusting in him we can have eternal life.

It does not say the the punishment of sin is death, It says the wages of sin is death. Romans 6:23; In other words if you live and continue to live a sinful life, your Spirit Man will die, this then becomes a spiritual death and you will spend eternal life in Hell. However, the gift of Life is through repentance and accepting Jesus Christ in your life.

The glorious thing about this is that the spirit man can be resurrected through confessing our sins,repentance, and accepting forgiveness from God our Heavenly Father. John 1:9 This qualifies one for eternal life with God.

The book of Romans 6:23 speaks of this Proverbs 11:19; Ezekiel 18:4;

If the life of flesh is in blood wherefore can it posses and immortal soul. That which is flesh is flesh that which is spirit (of the new nature) is spirit. Unfortunately religious folk have little understanding of the Koine Greek. The phrase “Wages of Sin is death” is translated into English with the objective genitive case. The Greek word wages here is “opsinia = ration” this is not a earned wage as the Greek word  “mithos” . This wage is an allotted portion or default ration passively allotted not only to mankind but all creation. The translation “sin” is an English invention of the Latin “sonts = guilty” from the proto Germanic “sunde”. The Greek is “amartias = bitter principal” from the prime root “amart” which is verb of the thematic aorist tense implying "the curse that entered the cosmos" in the indefinite past. The word “amartias” is a genitive case noun and when translated to English we would say “of SIN" or "of curse” however, this is not the case here. The word amartias has the definite article of the genitive case before it i.e. “tes amartias” so this reads in English of [the] sin or of the curse… translated the phrase reads “the allotted portion of [the] curse”. The last word in the phrase is “thanatos” = death. There is no [is] in the original this is an English addition for reading. Thanatos is a noun of the dative case so it reads in English “to death” but being the dative case it is not the direct object "of [the] sin ( amartias) is the object. In this case it points towards “of the curse (sin) and is connected to the phrase as a latent (concealed) genitive and in this case death is a latent genitive of the ruling principal. The text is better understood as ‘The default ration passively allotted due to the curse of Adam is death and death is the ruling principal.The Apostle then makes a contrast with the everlasting life offered Christ where grace is the ruling principal. He introduces the next phrase with "to.de" the conjunction of the aversive revealing the concealed antithesis of everlasting life.  Religious and pious people who insist that you earn death by committing actual sins as opposed to being born mortal and into a state of death know not the gospel nor are they born of the Spirit whose first work is to reveal to men that they are lost in death where sins are merely the fruit of the state of being. To avoid this consequence of death one needs not to born or believe the gospel of the glade tiding that Christ rose from the dead to give everlasting life.

Romans 6: 23

Romans 6:23 for the wages of sin is death:

Bible in Basic English 1 John 5:16
If a man sees his brother doing a sin which is not bad enough for death, let him make a prayer to God, and God will give life to him whose sin was not bad enough for death. There is a sin whose punishment is death: I do not say that he may make such a request then.
--
So not all sin is punishable by death.

But In order to be found blameless we have to walk to sanctification which means getting rid of all things in our lives that are not of God.God says if we destroy his temple(us) he will destroy us.that's why smoking causes cancer.