The chart doesn't have this built-in, so you will have to add these labels manually. I suggest using FillSceneGraph event for this. For example:

private void ultraChart1_FillSceneGraph(object sender, FillSceneGraphEventArgs e)
{
    if (e.Grid.Count <= 0) return;

    List<string> labels = new List<string>();
    IAdvanceAxis xAxis = (IAdvanceAxis)e.Grid["X"];
    IAdvanceAxis yAxis = (IAdvanceAxis)e.Grid["Y"];

    IChartData chartData = e.ChartCore.GetCurrentDataRef();
    int rowCount = chartData.GetRowCount();
    int columnCount = chartData.GetColumnCount();

    for (int i=0; i<rowCount; i++)
    {
        double value = 0.0;

        for (int j = 0; j < columnCount; j++)
        {
            value += chartData.GetValue(i, j);
        }

        Point location = new Point((int)xAxis.Map(i + 0.5), (int)yAxis.Map(value));
        Text label = new Text();

        SizeF labelSize = Platform.GetStringSizePixels(value.ToString(), label.labelStyle.Font);
        location.X -= (int)labelSize.Width / 2;
        location.Y -= (int)labelSize.Height;

        label.SetTextString(value.ToString());
        label.bounds = new Rectangle(location, new Size((int)labelSize.Width, (int)labelSize.Height));

        e.SceneGraph.Add(label);
    }
}