I read a lot on my Kindle and like to make highlights and notes while reading. You can read your annotations at https://read.amazon.com. However, Amazon only synchronizes the annotations for the books you have purchased through Amazon. I am unsure whether that is because of copyright issues or because Amazon does not want to help you with books purchased elsewhere. Both are equally probable. But annoying it is. (Even more so because I think Amazon is an unsympathetic company, and I prefer to use their offerings as little as possible. For stories about Amazon practices, read Cory Doctorow’s story, but a quick search on the internet will surface many more typical monopolist practices.)
Fortunately, the annotations are stored locally on the Kindle in a file called My Clippings.txt. When you connect the Kindle to your computer, you can browse the file structure on the Kindle and find this file.
I created a smallPython program to read this file’s somewhat cryptic format and convert it to a human-readable format. You can find it in a Gitlab repository here. The program currently requires some computer and Python literacy. When time allows, I will make it more user-friendly.