First of all you need to have the system's default Newsletters page assigned to a menu on your Console website. Go to WEBSITE > MENU > click on "Add Menu" and, in the pop-up window, name the menu (e.g. "My Newsletters"), select the Newsletters page from the drop-down list, and click on "Save".
Then go to your Console website, click on the newsletters menu you created, then on the specific newsletter issue. It will open in a new window; you can copy the link from there, and then paste it on your Facebook page.