aurelia01
It seems that you comment these lines of code which render the navigation in masthead:
$masthead = JLayoutHelper::render('joomla.content.masthead', $data);
$doc->setBuffer($masthead, array('type' => 'modules', 'name' => 'masthead', 'title' => ''));
?>
in the file: templates\ja_mono\html\com_content\article\default.php
Uncomment these code will help to show the navigation.