Is it possible for the knowledge of the Holy Quran, which was revealed in a clear Arabic tongue, to be different from that contained in the Preserved Tablet, the details of which are known only to the Prophet (PBUH) and those brought near [to God]?

We do not know what the speaker means by "the gnoses (ma'arif) of the Holy Qur'an," but if he means the Qur'an itself, then his statement is false; because it is truly the word of Allah, spoken by Him, Glorified be He, and revealed to His Prophet. As for his statement, "its details cannot be uncovered," if he means that the Prophet, peace and blessings be upon him, knew more about the Qur'an than other Muslims, then this is an accepted fact. People's understandings of the Book of Allah differ, so the well-grounded scholars know more about the Book of Allah than others. In the Hadith, it is stated: "Except for an understanding that Allah grants a man in the Qur'an." As for the mentioned supplication, it contains ambiguity, but generally speaking, there is no objection to supplicating for any permissible matter, as long as it does not reach the point of transgression.