Show Filters Attached to Hook

filtes.php

<?php
/* Attaching to Init because plugin files and theme files all have been loaded by this point and no output has been generated */
/* using anonymous function */
add_action('init', function(){
  /* replace wp_head with any filter or action hook */
  $hooks = digthis_see_hooked_actions('wp_head');
  var_dump($hooks);
});

function digthis_see_hooked_actions($hook = NULL){
  if(isset($hook)){
    global $wp_filter;
    return $wp_filter[$hook] ;
  }
  return false;
}

?>