for i:= 0 to DBCtrlGrid1.ComponentCount - 1 do
begin
  if (DBCtrlGrid1.Components[i] is TDBCheckBox) then
  begin
    inc(j);
    if (DBCtrlGrid1.Components[i] as TDBCheckBox).Checked then
      inc(k);
  end;  
end;

DBCtrlGrid1.Components[i].ClassType = TDBCheckBox

    j:= 0;
    k:= 0;
    for i:= 0 to ComponentCount - 1 do
    begin
      if (Components[i] is TDBCheckBox) and ((Components[i] as TDBCheckBox).Owner = DBCtrlGrid1) then
      begin
        inc(j);
        if (DBCtrlGrid1.Components[i] as TDBCheckBox).Checked then
          inc(k);
      end;
    end;
    ShowMessage('Проверено ' + IntToStr(i) + ' компонентов,' + #13#10 +
                'Чекбоксов ' + IntToStr(j) + #13#10 +
                'Выделено  ' + IntToStr(k));
  end;