Drupal 8 - get node object from field template

Inside your theme, add this function to THEMENAME.theme file, for example /themes/scriptun/scriptun.theme:

function scriptun_preprocess_field(&$variables) {
    $node = $variables['element']['#object'];
    $variables['node'] = $variables['element']['#object'];
}

Where scriptun is of course your theme name. With this little snipped you have {{ node }} variable available in any field twig file:

<div{{ attributes }}>
    This field is rendered on node: {{ node.id }}
    <div{{ title_attributes.addClass(title_classes) }}>{{ label }}</div>
    {% for item in items %}
        <div{{ item.attributes }}>{{ item.content }}</div>
    {% endfor %}
</div>