Working in the admin is quite a bit different from the front-end of a WordPress site. Most of the documentation you'll find online deals solely with the front-end. That can be frustrating when looking for something that should be simple and straightforward. 

In this case, I think you would use [`get_current_screen()`][1]. This returns the screen's ID, action, base, and other features of the admin page. 

From the codex on `get_current_screen()`:
> This function returns an object that includes the screen’s ID, base,
> post type, and taxonomy, among other data points

This doesn't work everywhere in the admin, so make sure you read the restrictions. 
  [1]: https://codex.wordpress.org/Function_Reference/get_current_screen