How to set hover in air in waypointV2Mission?

You can use START_STOP_FLY  to achieve this goal.

WaypointActuator waypointAction1Actuator = new WaypointActuator.Builder()
   .setActuatorType(ActionTypes.ActionActuatorType.AIRCRAFT_CONTROL)
   .setAircraftControlActuatorParam(new WaypointAircraftControlParam.Builder()
     .setAircraftControlType(ActionTypes.AircraftControlType.START_STOP_FLY)
     .setFlyControlParam(new WaypointAircraftControlStartStopFlyParam.Builder()
        .setStartFly(false)
        .build())
     .build())
   .build();

By using this action, the aircraft will hover in air. During the hover state, you can execute other waypointActions. After all waypointActions have finished, you can use a trigger to trigger the START_STOP_FLY action and fly to the next waypoint.

WaypointTrigger waypointAction2Trigger = new WaypointTrigger.Builder()
  .setTriggerType(ActionTypes.ActionTriggerType.ASSOCIATE)
  .setAssociateParam(new WaypointV2AssociateTriggerParam.Builder()
    .setAssociateActionID(associateActionId)
    .setAssociateType(ActionTypes.AssociatedTimingType.AFTER_FINISHED)
    .setWaitingTime(0)
    .build())
  .build();
WaypointActuator waypointAction2Actuator = new WaypointActuator.Builder()
   .setActuatorType(ActionTypes.ActionActuatorType.AIRCRAFT_CONTROL)
   .setAircraftControlActuatorParam(new WaypointAircraftControlParam.Builder()
      .setAircraftControlType(ActionTypes.AircraftControlType.START_STOP_FLY)
      .setFlyControlParam(new WaypointAircraftControlStartStopFlyParam.Builder()
         .setStartFly(true)
         .build())
      .build())
   .build();

WaypointV2Action waypointAction2 = new WaypointV2Action.Builder()
  .setActionID(++actionId)
  .setTrigger(waypointAction2Trigger)
  .setActuator(waypointAction2Actuator)
  .build();
waypointV2ActionList.add(waypointAction2);

After executing this action, the aircraft will cancel the hover in air action.