As I am sure you may have noticed, you can very easily forget where you have stored something in OneNote.
The good news is you can use the built-in search facility to find specific text in OneNote.
The search facility is found on the right-hand side of your Note window.
Simply key in your search text in the search box, and a pane will appear showing where your search text has been found.
Press ESC to close the search results pane.