How can I show a Joomla module on a product page

Hi,

There is no option like that with just HikaShop and Joomla.
However, there are two ways to go about it.
Supposing that you create one menu item per category to access your products, or that you create one menu item per product, and use the "canonical URL" setting of each category/product to point to that menu item, you could then use the "menu assignment" setting of the module to restrict it to the menu items (and thus the categories/products) you want.
But that's a bit cumbersome to setup and manage.
A simpler solution is to purchase and install Advanced Modules Manager Pro:
regularlabs.com/advancedmodulemanager
It has an integration with HikaShop so that you can restrict any module to any category of HikaShop. So it's easy to setup and manage.