Is my code correct to enqueue CSS on a specific page?

Try this:
I hope, It will works.

Explaination:

In below code in “is_page( 42 )” where 42 is page id of about page. So, if about page’s id will be 42 then it’s enqueue the stylesheet for that page only.

Also I define particular path for this CSS file by using wordpress function get_template_directory_uri().

function testimonial_style() {
  if ( is_page( 42 ) ) {
    wp_enqueue_style( 'custom_tooltip_frontend_css', get_template_directory_uri().'/path-to-my.css' ); 
  }
} 

add_action('wp_enqueue_scripts', 'testimonial_style');

Let me know How it help you.