1. You can use SelectedRows property to set the selected rows.
Example that selects the first row:
DayPilotGantt1.SelectedRows.Add(DayPilotGantt1.Tasks[0]);
There is a bug in the latest release that prevents this from working. It's fixed now in the latest sandbox build (8.1.3428):
http://www.daypilot.org/sandbox/
2. In the Gantt control (DayPilotGantt) there is no special object representing a row (as one row == one task). The Task object is used. However, BeforeTaskRender event handler BeforeTaskRenderEventArgs argument class has a special property for setting row-related properties: e.Row.
See also:
http://doc.daypilot.org/gantt/row-customization/