What is the inherited will that carries the legacy of the prophetic knowledge from Adam to Muhammad, peace be upon him, and who are its custodians after Muhammad, and what is its content and location, and is the succession still ongoing, and will it reach the awaited Mahdi?

There is no authentic evidence to prove the existence of a will that Adam (peace be upon him) bequeathed to his son Seth, which was then inherited by his descendants. Such a narrative has been mentioned in a lengthy tradition narrated by Abu Al-Sheikh in "Al-Azamah" from Muhammad bin Jaafar from his father, but it is not a marfu' hadith (definition) (a hadith directly attributed to the Prophet). The book "Al-Azamah" is known for the weakness or fabrication of its hadiths and traditions.