Impossible Scrabble Words
According to this reddit thread, the complete list of words in the allowed dictionary (which doesn't list words with more than 15 letters), the Collins Scrabble Words list from 2015, that you can't make with the available tile set is:


  BAZZAZZ
  BEZZAZZ
  PAZZAZZ
  PIZZAZZ
  PIZZAZZY
  BAZZAZZES
  BEZZAZZES
  PAZZAZZES
  PIZZAZZES
  KNICKKNACK
  RAZZMATAZZ
  KNICKKNACKS
  RAZZAMATAZZ
  RAZZMATAZZES
  RAZZAMATAZZES
  STRESSLESSNESS
  CLASSLESSNESSES
  POSSESSEDNESSES
  SENSELESSNESSES
  SUCCESSLESSNESS