How do I load a library defined with hook_library() on node/edit pages?
I would call drupal_add_library() in a hook_form_alter() implementation, like this:

function MODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if (isset($form['#node_edit_form']) &amp;&amp; $form['#node_edit_form') {
    drupal_add_library('MODULE', 'LIBRARY');
  }
}


This should ensure the library is loaded whenever a node form is displayed.

And using hints from Berdir to use hook_form_BASE_FORM_ID_alter and from kiamlaluno to use #attached:

function MYMODULE_form_node_form_alter(&amp;$form, &amp;$form_state) {
  $form['#attached']['library'][] = array('MODULE', 'LIBRARY');
}