Following is the web site environment I created:
I got it, its given in ScriptManager class itself.
System.Web.UI.ScriptManager.GetCurrent(this.Page);
Have you checked out this:
Working with ASP.NET Master Pages Programmatically
http://msdn.microsoft.com/en-us/library/c8y19k6h.aspx
Not sure what exactly you want here... you want to access the script manager of your master page or just the masterpage
?
You can access the master page by
Page.Master
in code behind
Or
using System.Web.UI;
ScriptManager ScriptManager1 = (ScriptManager)Page.Master.FindControl("ScriptManager1")
// to access the script manager of master page
or
Page.Master.Controls.Add(Your UserControl object)
// to add the user control in your master page