I would do this by making the notes mouse-over datatips, but it will depend a little on where your notes are kept. I will presume the notes are being stored in a virtual point, for simplicity. If you were going to do more complex things, you may consider creating another table in your database and treating them in keeping with your specific needs.
Using a virtual point, get the history of that point into a table via a history query and dragging over the point from the station tree. Now you should have a simple table with 'row', 'value' and 'timestamp' columns. Let's add a formula column to this table (I'll call it 'placeholder', and give it a simple script like 'return 10'. Now let's creating a second formula column, also with a simple script: 'return value' which should fill that column with a copy of the 'value' column (this step may or may not be necessary), and let's call it 'Comment'. Now click and drag the 'placeholder' column onto your chart, graph it against the timestamp (ts). There should be a flat line on the chart now at value 10. Navigate to the series we just added in the chart's properties. Consider using markers instead of a line, and weight/color them appropriately. Now go to the bottom section on the series, 'datatip' under 'Data Provider'. It probably says something like %nodeName% %xValue% %yValue%, and you can see those when you mouse over the chart. Let's change it to just %Comment%, click the green check mark, and mouse over the chart again. Your comments should now appear on your chart!
To see why we repeated the 'value' column into the 'Comment' column, try %value% in the tooltip.
Here's a page where this has been done: http://mangoautomation.net:8081/dglux/view?dgml=dgml%2FTempates%2Feventchartdemo.dgml