Why my javascript code not working for the dashboard of wordpress admin?

You need to add your script into your functions.php

function my_theme_scripts() {
    wp_enqueue_script( 'my-great-script', get_site_url() . '/js/my-great-script.js', array( 'jquery' ), '1.0.0', true );
}
add_action( 'admin_enqueue_scripts', 'my_theme_scripts' );

Then, in your file (my-great-script.js), you will have to have something like this:

jQuery('.dash_appoint_r').on('click', function(){
    alert('hello');
});