Point your subdomain (shop.d9studios.net) to a directory in your public_html directory (or whatever it's called in your case) called 'shop'.

Put your Zen Cart system in that directory.

Edit your config files (not sure what they're called OTOH) to point to the shop folder. There's plenty of info around on how to successfully move a system from one folder to another (in the forum and the FAQs). You'll find there's two files to change - one for the catalogue and the other for admin - each with some URLs and physical paths.

As you're not relocating a database all of that should be ok.