How do I check the content of variables passed to a template file?
You can follow document. 


  To dump only the available variable keys use:


{{ dump(_context|keys) }}


In this case you can use:

{{ kint(node|keys) }}


Or you can follow topic


  Create a /modules/contrib/devel/kint/kint/config.php file and add /
  modify the line $_kintSettings['maxLevels'] = 3; (by @mdrummond on
  Slack)


The best way: install module twig_tweak and using twig function

{{drupal_dump(node)}} to dump variables.