Knotes support reading notes from Kindle App. All you need to do is exporting notes to your email, and import the downloaded attachment to Knotes.
1.Open a book in Kindle App, open [MY NOTEBOOK].
2.Select [Export Notebook to] > [Email], and send notes to your email address.
3.Ahead to your mailbox and download the HTML attachment.
4.Open the sync menu of Knotes, select [Manual Import] > [Kindle App exported file].
5.Choose the HTML file that you just downloaded.