Here is how you create a Forward this message to a friend link in an email.
The dynamic that the WYSIWYG creates is dynamic and will populate a URL that is specific to the email message that the link is contained in. The finished URL will have an added parameter in the URL to define which message should be forwarded (&msgId=####). This parameter is generated by the system when the emails is sent. You can't specify the message ID yourself, the system will always use the message ID of the message the link is contained in.