Understanding search traffic and keywords for my Shopify store

You can install an SEO app and connect it to your Google account. It will let you discover your most popular SEO keywords in addition to many other SEO features. SEO King (https://apps.shopify.com/seo-king) is a good option but there are also some other good apps.

Use Google Search Console. It is a free service from Google that helps you monitor your website's appearance in search results. You'll be able to see which queries bring users to your site and also analyze your site's impressions, clicks, and position on Google Search.