In Moses 6:46 we read:
For a book of remembrance we have written among us, according to the pattern given by the finger of God; and it is given in our own language.
The idea that Enoch kept a book of remembrance containing the actions of the people is also attested in the Book of Giants, 1 Enoch, the Testament of Abraham and in Jubilees.
Where did Joseph get all this information from?
See: