/**
 * Implements hook_theme_suggestions_HOOK_alter().
 */
function mytheme_theme_suggestions_paragraph_alter(&$suggestions, $variables) {
  $paragraph = $variables['elements']['#paragraph'];
  $parent = $paragraph->getParentEntity();
  if ($parent) {
    $suggestions[] = 'paragraph__' . $parent->bundle() . '_' .  $paragraph->bundle();
  }
}