how to achieve the zooming feature in scheduler control ???

You can find the source for this example in the DayPilot package: Demo/Scheduler/Default.aspx.

This functionality is an example of refreshCallBack client-side method:

1. Use the BeforeTimeHeaderRender to change the headers. Include hyperlinks that call dps.refreshCallBack(newDate, newDays):

    protected void DayPilotScheduler1_BeforeTimeHeaderRender(object sender, DayPilot.Web.Ui.Events.BeforeTimeHeaderRenderEventArgs e)
    {
        if (e.IsColGroup)
        {
            int days = (int) Math.Floor((e.End - e.Start).TotalDays);

            DateTime outStart = DateTime.MinValue;
            int outDays;

            switch (DayPilotScheduler1.CellGroupBy)
            {
                case GroupByEnum.Hour: // day, switch to week
                    outStart = Week.FirstDayOfWeek(e.Start, DayOfWeek.Monday);
                    outDays = 7;
                    break;
                case GroupByEnum.Day: // week, switch to month
                    outStart = new DateTime(e.Start.Year, e.Start.Month, 1);
                    outDays = DateTime.DaysInMonth(e.Start.Year, e.Start.Month);
                    break;
                case GroupByEnum.Week: // month, switch to year
                    outStart = new DateTime(e.Start.Year, 1, 1);
                    outDays = DateTime.IsLeapYear(e.Start.Year) ? 366 : 365;
                    break;
                case GroupByEnum.Month: // year, dont switch
                    outDays = 0;
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }

            if (days >= 1) // do not zoom into greater detail than one day
            {
                e.InnerHTML = String.Format("<a href="javascript:dps1.refreshCallBack(new Date(\"{0}\"), {1})" title="Zoom in">{2}</a>", JsDate.FormatDateTime(e.Start), days, e.InnerHTML);
            }

            if (outDays > 0) // do not zoom out if we see the whole year
            {
                e.InnerHTML += String.Format(" (<a title="Zoom out" href="javascript:dps1.refreshCallBack(new Date(\"{0}\"), {1})">up</a>)", JsDate.FormatDateTime(outStart), outDays);
            }
        }
    }

2. Handle the Refresh event on the server side and update the StartDate and Days properties using the sent values:

    protected void DayPilotScheduler1_Refresh(object sender, DayPilot.Web.Ui.Events.RefreshEventArgs e)
    {

        DayPilotScheduler1.StartDate = e.StartDate;
        DayPilotScheduler1.Days = e.Days;

        if (e.Days > 31) // year
        {
            DayPilotScheduler1.CellGroupBy = GroupByEnum.Month;
            DayPilotScheduler1.CellDuration = 1440;
            DayPilotScheduler1.CellWidth = 20;
        }
        else if (e.Days >= 28) // month
        {
            DayPilotScheduler1.CellGroupBy = GroupByEnum.Week;
            DayPilotScheduler1.CellDuration = 1440;
            DayPilotScheduler1.CellWidth = 30;
        }
        else if (e.Days > 1) // week
        {
            DayPilotScheduler1.CellGroupBy = GroupByEnum.Day;
            DayPilotScheduler1.CellDuration = 60;
            DayPilotScheduler1.CellWidth = 20;
        }
        else // day
        {
            DayPilotScheduler1.CellGroupBy = GroupByEnum.Hour;
            DayPilotScheduler1.CellDuration = 15;
            DayPilotScheduler1.CellWidth = 20;
        }

	// update DayPilotScheduler1.DataSource and call DayPilotScheduler1.DataBind() here
	// ...
        DayPilotScheduler1.Update();
    }