You can find the database
currently in use by Cintanotes looking into menu
File >
Notebook... and then look for
Notebook File: there you can read the full path to the notebook file. The notebook file is named cintanotes.db and it is the file which holds all your notes.
Now, if you can't see your notes and only have an empty list, maybe, while updating, CintaNotes failed to locate your old database. If this is what happened, you have to manually point CintaNotes to the old database, thus you would click the ellipsis button "..." and browse to the old file using the "Browse for CintaNotes Notebook File" dialog box.
But if you don't know or don't remember where the old database is, and so you don't know what to pick in this browse dialog box, I would suggest the use of a third party tool like
Everything which is easy to use and available in a portable version. If we search for
cintanotes.db in Everything it would help to identify and show the path (we can read it in the search results) to use in the dialog box I said in the previous paragraph.
Finally, it's rare, but if you upgraded from a very very old CintaNotes beta release, we talked about the problem in this topic
viewtopic.php?f=6&t=1036. But feel free to ask if you need further assistance.