If you have your Shopify store hooked up to your Snapppt account, then you have the ability to look up a product by it's name. But, the destination field for a Hotspot also supports simply entering a URL, and this is what you'll need here. To link to a specific variation, please follow these steps:
Visit the Product page in your store
Using the variation dropdown, select the variation you'd like to link to. Upon doing so, you'll notice the URL updates to refer to the variation.
Copy and paste this URL into the Hotspot destination field on Snapppt
Note that the end result is the same as if you had looked up a product by name - the product image and price data will still be pulled in.