If you want to create a link from somewhere to send a private note, then you need the user_id of the user you want to send the private note to.
The default URL for the private note would be:
Where 2 in this case is the user you're wanting to send the private note to.
There is a caveat though - the link to this page must come from a page within the site or you will end up with an "invalid url validation error" due to Jamroom's CSRF form checking.
To make sure this doesn't happen, and you can send your email note to one of your followers, you need to set a cookie on the page where the link is.
An example of that is below: