The role of Mahijah in the Book of Moses is strikingly similar to his role in the Book of Giants.
Jeffrey M. Bradshaw explains:
In the Book of Giants, we read the report of a series of dreams that troubled the gibborim. The dreams “symbolize the destruction of all but Noah and his sons by the Flood.” In an impressive correspondence to the questioning of Enoch by Mahijah in the book of Moses, the gibborim send Mahawai to “consult Enoch in order to receive an authoritative interpretation of the visions.” In the Book of Giants, we read:
[Then] all the [gibborim and the Nephilim] … called to [Mahujah] and he came to them. They implored him and sent him to Enoch, the celebrated scribe and they said to him: “Go… and tell him to [explain to you] and interpret the dream…”
Cirillo comments: “The emphasis that [Joseph] Smith places on Mahijah’s travel to Enoch is eerily similar to the account of Mahawai to Enoch in the [Book of Giants].”– Jeffrey M. Bradshaw – KnoWhy OTL05C — Could Joseph Smith Have Drawn On Ancient Manuscripts When He Translated the Story of Enoch?
Where would Joseph Smith have read this about Mahijah?