I have written a grammar for hex editors like Synalyse It! and Hexinator for the reMarkable note files.
The grammar can parse properly only v5 of reMarkable files. This version stores each page in a different .rm file.
You can find your notes at:
$HOME/.local/share/remarkable/xochitl/
There are plenty of articles about reMarkable tips and tricks, but if you are just starting with the behind the scenes of this device, I can recommend this article from the same guy who reverse engineered reMarkable file format.