procedure TfrdParentTest.actOpenUpdateExecute(Sender: TObject);
begin
  inherited;
  FCountDS := 0;// обнулить счётчик

  qData.Close;
...
добавление параметров, построение SQL запроса
...
  qData.Open;

  ShowMessage(FCountDS.ToString);// выдает 2
end;

procedure TfrdParentTest.dsDataDataChange(Sender: TObject; Field: TField);
begin
  inherited;

  if qData.Active then
    inc(FCountDS);//увеличиваем счётчик
end;

  private
    FCountDS1: Integer;

    { Private declarations }
  public
    { Public declarations }
  end;

var
  frdParentTest: TfrdParentTest;

implementation

{$R *.dfm}

procedure TfrdParentTest.DataSource1DataChange(Sender: TObject; Field: TField);
begin
  inherited;

  if UniQuery1.Active then
      inc(FCountDS1);
end;

procedure TfrdParentTest.UniToolButton13Click(Sender: TObject);
begin
  inherited;
  FCountDS1 := 0;
  UniQuery1.Close;
  UniQuery1.Open;
  ShowMessage(FCountDS1.ToString);
end;

procedure TfrdSessions.dsSessionsDataChange(Sender: TObject; Field: TField);
begin
  if cdsSessions.Active then
    inc(ccc);
end;

procedure TfrdSessions.actOpenUpdateExecute(Sender: TObject);
begin
  if not ReadMonitorUsers(true) then
    exit;

  ccc := 0;
  GetSessions;
  UniStatusBar1.Panels[0].Text := ccc.ToString;
end;