Can you detect items inside of another item?

I'm trying to make an equipment menu akin to baubles/curios since I genuinely cannot for the life of me get curios to work in my mod, and I know you can't tie an inventory to the player since it clears whenever the menu is closed, which is why I'm wanting to make something like an accessory pouch , but I can't seem to find out how to, if I even can, detect what items are in another item's inventory when it's closed.

Any help is appreciated !