Where can I find in database that page (panel) is disabled?
Panel pages requires Page Manager module which comes with Ctools Module.... Below function in page_manager/page_manager.admin.inc is responsible for enable / disable action...

function page_manager_enable_page($disable, $js, $page) {
  if (!isset($_GET['token']) || !drupal_valid_token($_GET['token'], $page-&gt;task_name)) {
    return MENU_ACCESS_DENIED;
  }
  if ($page-&gt;locked) {
    if ($disable) {
      drupal_set_message(t('Unable to disable due to lock.'));
    }
    else {
      drupal_set_message(t('Unable to enable due to lock.'));
    }
  }
  else {
    if ($function = ctools_plugin_get_function($page-&gt;subtask, 'enable callback')) {
      dpm($function);
      $result = $function($page, $disable);
      menu_rebuild();

      // We want to re-cache this if it's changed so that status is properly
      // updated on the changed form.
      if (!empty($page-&gt;changed)) {
        page_manager_set_page_cache($page);
      }
    }
  }

  // For now $js is not actually in use on this.
  drupal_goto('admin/structure/pages');
}


When a panel page (Custom Created , Not default pages that comes with module) is enabled or disabled below function is called in ctools/page_manager/plugins/tasks/page.inc...

/**
 * Callback to enable/disable the page from the UI.
 */
function page_manager_page_enable(&amp;$cache, $status) {
  $page = &amp;$cache-&gt;subtask['subtask'];
  ctools_include('export');
  ctools_export_set_object_status($page, $status);

  $page-&gt;disabled = FALSE;
}


You can find panel pages details inside variable table under the variable 


  default_page_manager_pages


When Disabled

a:1:{s:15:"test_panel_page";b:1;}


When Enabled

a:0:{}


Default pages that comes with module enable / disable status also stored in variables table...