Hi Karen,
Are you referring to Last Note and Has Notes? If so, these are pointing to the Updates Section of the Task. Any comms that occur at the Task level will populate this. Last Note can be tricky is it will only show the most recent Update conversation.
If there is another "Notes" field you are referencing, this could be a custom field. You can look for this in the Custom Forms>Fields section of Setup and do a search on that field name to see what Custom Form this field is attached to.
I hope this was helpful.
-Joaquin