Thou knowest, O Death, the fire-sacrificef which leads us to heaven; tell it to me, for I am full of faith. Those who live in the heaven-world reach immortality,- this I ask as my second boon."

In plain words: For his second wish, Nachiketas asks Death to teach him the fire ritual that leads to heaven. He says he truly has faith. He has heard that those in heaven do not die.