How do I tell what traffic comes from Pinterest and what the search words were
You should use the official Pinterest and Shopify integration. This requires a Pinterest Business account, an Advertiser account (with a credit card linked), and a paid Shopify subscription.
Once connected via the API, data will pass between the stores, allowing you to see “referral traffic.” This helps you identify which keywords lead to purchases and which ones lead to other conversions like email signups. If you don’t use the integration, Shopify will still show basic social referral data, but it won’t be nearly as granular.