Yehuda just finishes telling Yosef the whole story including that his father is alive, so what exactly was Yosef's question. In addition, Rashi quotes the medrash that this was a great תוכחה. What exactly was the תוכחה?
The Beis Halevi explains as follows. Yosef told his brothers you claim that you are so concerned about your fathers health, yet, I am Yosef is my father still alive? Meaning, he asked them if you really cared for your father how could you put him through the pain of of my disappearance. He exposed the hypocrisy of Yehuda's claim through Yehuda's own actions. Now we also understand why this is called a תוכחה as well.
The Beis Halevi says that this is what will happen as well when a person goes up to שמים after 120. Whatever excuses he gives for not doing mitzvos or aveiros will be shown to be hypocritical by his own actions. I will give 1 simple example. A person doesn't go to minyan on Sunday mornings, he claims that while he understands the importance of davening with a minyan he is just so tired he needs to sleep late. In שמים they will show him that whenever he had some other important event on Sunday morning he always managed to get up and therefore goign to a minyan was really not that important to him.