Jesus told Nicodemus that no one can see the kingdom of God unless he is what?

Answer: Born again

Jesus said, "No one can see the kingdom of God unless he is born again." Nicodemus asked how a man can be born when old.

“Jesus replied, “Truly, truly, I tell you, no one can see the kingdom of God unless he is born again.” “How can a man be born when he is old?” Nicodemus asked. “Can he enter his mother’s womb a second time to be born?””— John 3:3-4 (BSB)