How to access the node title within a field template?
He wants to get the node title in the file link template (I assume that is file-link.html.twig). 
You can implement the hook template_preprocess_file_link() in your mytheme.theme file, get the current node and pass its title to twig, something like:

function mytheme_preprocess_file_link(&amp;$variables) {
   $node = \Drupal::request()-&gt;attributes-&gt;get('node');
   $variables['node_title'] = $node-&gt;getTitle();
}


Then, in file-link.html.twig:

{{ node_title }}