functions like add_submenu_page() ask for a capability when they are called, as in de code below:
add_submenu_page( $parent_slug, $page_title, $menu_title, $capability, $menu_slug, $function );
$capability contains the capability required for this menu to be displayed to the user.
When you want to know wich Roles and Capabilities are used in a theme or plugin, you could take a look in de code and search for these kind of functions.
Also, if you downloaded a theme or plugin, you could give it a try to search for this information on the developers website.