Hello,
You can do this using SWS Extension.
First, you go on
https://sws-extension.org and download the extension and install it.
Then you open reaper and you can use the function "Notes" in the Extensions menù at the top.
Here you can setup notes for different things such as tracks, regions, project, items ecc...
Every time you change a selection the Notes window will show you notes relative to the selectded element for the selected mode.
You can also Lock Notes to avoid unwanted changes and of course you can dock the window anywhere