if You want to get all tag/category of custom post types then use the below code.
$terms = get_terms([
'taxonomy' => 'testimonial_tag', // here you can add you custom taxonomy name
'hide_empty' => false,
]);
$result = new WP_Query($terms);
If you want to get a particular custom field value from a particular taxonomy/tag then use below code
echo get_field('tes', 'testimonial_tag_18');
eg : get_field('custom-field-name', $term->taxonomy . '_' . $term->term_id);