Why was it that only 'Umar ibn al-Khaṭṭāb knew about the verse of stoning, and how can one respond to those who ask about this?

The verse of stoning is among the verses whose wording was abrogated but whose ruling remained. Thus, it is no longer a verse of the Holy Quran, but its ruling persists, and this is why it was not written in the Mus'haf. 'Umar ibn al-Khattab was not the only one aware of this verse; its affirmation was reported by a group of Companions, such as 'A'ishah, 'Ali, Ubayy ibn Ka'b, and Zayd ibn Thabit. 'Umar affirmed this verse on the minbar during the Friday sermon, and the senior Companions approved of it, with none of them denying it.