//add parent querystring to subpages
$('a[href^="/example/"]').each(function(index, element) {
  var parentAttr = $(this).attr('href') + '?parent=' + Drupal.settings.nodeinfo.nid;
  $(this).attr('href', parentAttr);
});

http://mysite.com/example/subpage#anchor-name

http://mysite.com/example/subpage#anchor-name?parent=123

http://mysite.com/example/subpage?parent=123#anchor-name

var components = parse_url('http://username:password@hostname/path?arg=value#anchor');

{
  scheme: 'http',
  host: 'hostname',
  user: 'username',
  pass: 'password',
  path: '/path',
  query: 'arg=value',
  fragment: 'anchor'
}

$('a[href^="/example/"]').each(function(index, element) {
  var components = parse_url($(this).attr('href'));

  var newUrl = components.scheme + '://' + components.hostname + '/' + components.path + '?parent=' + Drupal.settings.nodeinfo.nid + '#' + components.anchor;

  $(this).attr('href', newUrl);
});