Clock tasks are Ms.SharePoint.Administration.SPJobDefinition things. To make a timer job, one should make a new category that gets from SPJobDefinition. Clock tasks can be implemented by using Features, customized programs, Power Spend, or customized STSADM orders.
Debugging Timer Service: User needs to attach debugger with OWSTIMER.exe process. This is the “Windows SharePoint Services Timer" service.
Debugging Event Receiver: User can attach Visual Studio to the w3wp.exe process and simply put a breakpoint in the event handler code. Alternatively, use System.Diagnostics.Trace to write out information to a log