Loop through the terms of a custom taxonomy and get their stuff. This outputs a list of terms from a custom taxonomy and lists their “ID’s”.

// loop through terms of a custom Taxonomy
$getArgs = array(
	'parent'       => 0,
	'order' => 'DESC',
	'orderby' => 'count',
   	'hide_empty'    => false,
);
$taxonomy = get_terms('MY_TAX', $getArgs);
			
foreach ($taxonomy as $term) { 
            
	 echo '<li>' . $term->term_id . '</li>';
                
}