How can I extract my MacBook Pro Notes files so that the data becomes "normal" again after my computer's file system crashed?

My MacBook Pro from ca. 2011-2013 or something kind of "crashed" - the computer's file system was ruined - when I did a manual forced shutdown because the Notes app was not responding. When I turned it back on again repeatedly, it was in MacOS Recovery Mode and I sent it in to a computer expert who's having a look at it. He's been able to save/restore many documents - Pages documents, sound files, pictures and videos etc - and also says that the data isn't gone, it's just like scrambled or arranged differently now or something. However: He doesn't know how to extract the files from my Notes app, which are my most important documents. He says that there could be several ways to do this but he's not an expert on this particular Mac file system or computer model/operation system. How does one extract the Notes files and get my data back as readable Notes files?