The Omnisearch feature in Jetpack enables you to search your entire WordPress database from a single field in your dashboard, including posts, pages, comments, media, and custom fields.
Omnisearch lets you search posts and pages on your site, as well as custom post types, comments or the media library. You can access the Omnisearch feature from the search icon right near your profile.
Searching in this field will return a result of your search terms across all your WordPress content. Note that this feature is only accessible while you’re logged into the administration area with Jetpack connected—and not for visitors to your site.
You do not need to do anything to to enable Omnisearch, you will find it in your toolbar once you setup Jetpack. If you need to search for content within the admin, do it easily using the Jetpack Omnisearch feature.