How can I assign the Commerce Product SKU as the Path Alias?
Pathauto should give you enough flexibility to do that.

Once your "product" content type has a commerce_product_reference field linked to it (let's call it "field_product"), all fields attached to your "product variation type" should be available as tokens like this:

[node:field-product:product-id] or if you created a specific field to store the value [node:field-product:field-sku].

You probably know it but patterns can be configured from here : admin/config/search/path/patterns.