can we assign value to parent control in DayPilotScheduler1_BeforeCellRender(object sender, DayPilot.Web.Ui.Events.BeforeCellRenderEventArgs e)
or is there any way to assign value to parent control in asp.net webforms
Yes, you can use BeforeCellRender to set the content of every grid cell.
Yes, it's possible in ASP.NET WebForms as well. If you scroll down the page, you'll find a section with example for ASP.NET WebForms.