You can find out how many people visited a product page on Shopify by looking at the Product analytics. 
 
Viewing Product Analytics
  1. From your Shopify admin, click Products.

  2. Click the name of the product that you want to view.
  3. On the Product details page under "Insights", click View Details. 

 
Please Note: You may not find any data under Insights if the product does not have any recent sales yet. In this case, when you're doing the Forecast Analysis, you can look at your Facebook ads reporting to find out the number of link clicks you have to your specific product page.