Please be sure to know how to use shared SSL for your primary domain, first. Refer to How to set up and use your shared SSL for more details.
To use shared SSL for an addon or subdomain, you will use the primary domain's URL followed by the subfolder path.
EXAMPLE: For an addon domain named domain2.com and its associated folder public_html/domain2.com/
From the previous article, suppose the shared SSL URL is https://secure123.hostgator.com/~bill/
The correct format for your addon domain will be https://secure123.hostgator.com/~bill/domain2.com/
Is there another way to use shared SSL without showing the folders? I don't want anyone to know this is an addon domain.
With shared SSL, this is the only working method. The domain must always show (in our example) secure123.hostgator.com or it will cause browser/pop-up warning messages which discourage visitors from viewing your site.