I use inkpad2, so I probably can help a bit
Here I attached some files:
1. Zipped files/folder of how the notes are stored (html, plus folder with screenshot, svg of the annotation)
2. How it look like if opened directly in calibre
3. How it look like in inkpad
ps: when you switch to device's book in calibre, the notes have the same title as the book. You can't import the note to calibre library as it will say there is a book with the same title (the actual book), and ask you whether you want to overwrite (the actual book and replace it with just the notes
)