As mentioned in a comment, media is actually a special 'post', so the media only belongs to the sub-site, and is not easily accessible from the subsite.
But there are methods to go though all subsites and display the media from all subsites on a single page in any subsite. I do this with my Multisite Media Display plugin (https://wordpress.org/plugins/multisite-media-display/ ), which first enumerates all subsites into an array, and then queries each subsite to display the images within that subsite. It does the work via a shortcode you display on a post/page. I use it to monitor the media on all subsites to ensure that the media meets the site's standards. And, if logged in as the super-admin, each image links to it's 'edit' page, which allows me to rotate pictures as needed.
As with all plugins, the code is 'open source' (and the plugin is free/full-featured), so if you wanted to 'roll your own', you could use the code processes that I use (which I gathered from the googles, and then tweaked the code into my plugin). I couldn't find a plugin that did what I needed, so wrote it for my own use. (And then I made variations to display posts or comments from all subsites via a shortcode.)
The plugin has options to specify subsites and other parameters, so you can 'filter' the output to what you need.
You are welcome to use the code in the plugin to make your own plugin that will do exactly what you need.