Google Search is testing a new notes feature where you can add your own notes to the search results and also see the notes others have left on that search result. This is a Search Labs experiment that you need to opt into and launched in the US and India on mobile and within the Google app.
You can add and view notes on both Google Search and in Google Discover.
If you opt into this Search labs experiment you will see a new “add note” icon on search results. If others left notes, you will see the number of notes for a specific search result.
Clicking on add note will give you the ability to add a note that anyone else can see. While clicking to view the notes will let you see other notes other searchers left on that search results.
Here is a screenshot of that add note and notes icon:
Then when you click to view the notes, you are taken to a listing of these notes, the notes are ranked in order or relevancy and usefulness. Here is the notes list view:
Here is the detail note view for a single note, you will see in the footer of each note screen, there is a link to the source landing page.