In QV11 at least, when creating the note, in the top left top right corner there is an icon of two people which when clicked allows you to specify "Who can see this note" and the options are ...
Anyone who can see the object
I've never tested it, and don't think you can specify groups under 'Specific People'. It might be easier to create different objects for the groups and control visibility to the users via conditional show of the object and the last option above.
The note is written to the .Shared file of the document on the server - the note is clear text so could be read out of there if that's what you wanted (just look for the AT prefixed object refererences).
EDIT: icon is top right not top left.