wp_editor add media button not working

I will assume that you are creating a custom admin page at ?page=add-quiz, in this case before calling the wp_editor function you also have to enqueue the CSS / Js files for it with the wp_enqueue_media() function.

So at the end you should have

wp_enqueue_media();
wp_editor( '', 'instructions', $settings = array('textarea_name' => 'instructions', 'textarea_rows' => '5') );

A clever way to do it would be inside an action like

function prefix_my_custom_admin_scripts() {
    wp_enqueue_media();
}
add_action('admin_enqueue_scripts', 'prefix_my_custom_admin_scripts');

Again assuming that you don’t have this hook already.