It’s not that easy to find the top pages of any website, but most of the SEO tools will give you an approximate idea though. You can use the trial versions of SEMrush, Moz or Ahrefs to find them. They work well. You can easily analyze your competitors’ keywords or top posts. But if you need to get a basic idea without signing up anywhere, then I would suggest Alexa.
At the right side, you can see the top 5 keywords from search engines. These are the search keywords which sends traffic to this website. If you want to find the keywords for which you are ranking for, you can use Google Search Console for that.