All your private notes are saved during your 1-on-1 meeting. You'll find them in the same meeting where you jotted them down.
Go to ‘1-on-1 Meetings’ and open the 1-on-1 meeting for which you had taken private notes. Scroll down to Private Notes section and your notes will be saved there.
If you had written down your notes for a past 1-on-1 then scroll the main 1-on-1 meeting page and look into the ‘Past 1-on-1s’ section. You will find your private notes in that particular 1-on-1meeting.