Who documented biblical events before Moses? From the creation until the time of Moses, who documented the events? Abraham? Prophets? Priests?
This is a great question, and one might have thought that we have nothing at all to go on, except guesswork.  But actually we do have something to go on, and that is the existence of Hebrew words in early Genesis which are loan-words from other languages.
According to Robert D. Wilson, throughout most of the first five books of the Bible the predominant language from which words are loaned is Egyptian.
But there are no Egyptian loanwords in the chapters prior to the descent into Egypt.  The loanwords in the first chapters are from Babylonian and Sumerian, suggesting that either Moses simply fully incorporated something already written into Genesis or he summarised something already written - and what he included was something which had been written by an (unknown) author who lived in southern Mesopotamia/modern southern Iraq.
Personally, I think the most likely means, even the only means, by which he could have received these writings was via the Hebrew community, and they received them from Abraham.  (Even though Moses would have had access to the libraries of Egypt these would not have contained divine/prophetic literature, or even if they had contained prophetic literature it is still necessary to have a reliable witness to authenticate them.  The authenticating witness to these writings in my opinion could only be the Hebrew people.)
For more information on this look at &quot;Foreign words in the Old Testament as an Evidence of Historicity&quot; by Robert Dick Wilson,and scroll down to start reading from page 210.
(The English of) Hebrew words known to be of Babylonian origin are: Adam, Abel, Methusaleh, Amraphel, Chedorlaomer, Tidal, Abram, Sara, Babel, Ur, Erech, Haran, Havilah, Calah, Padan, Ninevah, Eden, Shinar, to cover with pitch, pitch, cherub, oven, to dwell, flood.
(The English of) Hebrew words known to be of Sumerian origin are: Arioch, Gihon, Pishon, Hiddekel, gopher-wood, cereal, canal.
The whole of this work by R.D. Wilson is worth studying but its not an easy read.
Foreign Words in the Old Testament as an Evidence of Historicity by Robert Dick Wilson:-
https://biblicalreadercommmunications.files.wordpress.com/2017/01/foreign20words20in20the20ot20as20evidence20of20historicity20192820ptr2026-2.pdf