For most WordPress based sides, you can look at the classes on the body tag to find out what kind of content is being shown, a single post, a post archive, the front page etc. In your case, it’s post-template-default single single-post postid-2897 single-format-standard wpb-js-composer js-comp-ver-5.0.1 vc_responsive, so this is a single post that is shown (most of those classes come out of get_body_class, it’s worth a look at the code to fully understand how that works).
To find the file responsible, look at the template hierarchy and check your theme which files exist.
If you change your original theme directly, you’ll lose those changes when you update to a newer version. Instead, create a child theme to adapt the original theme to your needs. This allows you to override certain files but keep the rest as it is.