Are you asking how to add custom content to S4S so you can clone the custom content? Go to your C drive, or wherever Sims4Studio installed--in my case, it's the C drive but some people have more than one hard drive. Assuming you have one hard drive the file path you need is C:/Program Files (x86)/Sims4Studio/Recolorables. Just drop the custom content files you want to clone in that folder and it will show up in Sims4Studio.
Edit: I just realized you asked about an item from the game. In the top right-hand corner of S4S you'll see "show debug items." Click the little box next to it and S4S will display the game items that aren't normally available to players. Just do a search on "petmate" and you'll find what you're looking for.