Kresimir,
I am assuming that this is based on the Progress UPdate Reports that are sent out to Resources. The Note would be added to the Notes Panel of the Task. There is no way (out of the box) to have the Project Manager (or other user) notified of this information but you can create a Customization. A workflow rule that sends an email to someone like the Project Manager when a new Note is created.
Go to Settings-->Configure and select Note (under Collaboration Items) from within the Item Types on the left pane. Create a new Workflow and use the runtime 'When a record is created, or when a record is edited and did not previously meet the rule criteria'. Then provide any Evaluation Criteria you want. The action will be send email and that will allow you to specify who you want the email to be sent to. You can specify a specific user or use a field variable like $ProjectManager that way no matter the Resource or Task this rule runs on, the Project Manager of the associated Task/Note will be informed.
Sincerely,
Boris