Using the above link, searching the forum or asking questions.
You are obviously going to need 2 rules. Both with the Automation Command Name with the name Task Note (as an example). You will need to add another constraint to each rule to select the correct rule. You are not restricted to the drop down options, you can use a report, printer tag, settings value, etc (depending on the rule event). In your case you want to know if a tasks’ note field Is Null or Is Not Null. That would require a report. Something like this: {REPORT OPEN TASK DETAILS:TSC.Notes:T.Identifier="<id number"}
or something similar. (This is assuming you have some type of task identifier tied to the ticket.)
Assuming you want to edit a note, you probably want to use a prompt. This post offers a lot of useful information:
Your prompt is going to look something like this: [?Notes;;{REPORT OPEN TASK DETAILS:TSC.Notes:T.Identifier="<id number"};OC;]
This will load the report results as the default text.
Depending on which Task field you are using, you are going to have to mask some characters. If you are using a Custom Field you are going to want to mask out both types of quotes, pipes and comma’s. If you are using Content field as notes, I think you just have to mask out pipes and comma’s. The reason is that these characters mess up the report results or will not be written to the database.