code: def current_watermark(self):
      return self._j_timer_service.currentWatermark()
  
imports: from pyflink.datastream import TimerService
  from pyflink.fn_execution.datastream.timerservice import InternalTimerService, N
label_desc: Use image node_id 3 for calling the TimerServiceImpl obj's underlying member method code with example usage: obj.current_watermark() and returns: self