My enqueue admin style function doesn’t work because of ?=ver

It has nothing to do with version. First of all you have a typo in constant name: PULUGIN_URL. Even if you change it to PLUGIN_URL, it will not work, because such constant does not exists. When you do it from within plugin, use proper function. In your case it should be: plugin_dir_url(__FILE__). Your code should be:

function wpse_enqueue_style() {
    wp_enqueue_style('pk-admin-css', plugin_dir_url(__FILE__) . 'css/admin.css');
}
add_action( 'admin_enqueue_scripts', 'wpse_enqueue_style' );