Are you currently recording the time when notes are added? You will need to do this first.
Next you will need to select from your clients table where the userID matches the currently logged in user, you will then need to join the clients table with the notes table where the client id from the clients table matches the client id in your notes table. Once you have done this you can order by the date date/time column in descending order for the notes and limit it to 5 results. This will give you the last five notes for a given user.