If you want your sketch to trigger the watchdog then you just need to enable the watchdog and then not reset it. It would be helpful if you designed your sketch to do something obvious when it resets so that you can tell when the reset has occurred, such as flashing the onboard LED in a recognisable pattern.
AMPS-N:
Since i am new to this can some one share me the COde for doing this...
Since you're new to this, why don't you just try writing some code and try it for yourself? There's nothing complex or difficult in what you're trying to do and plenty of other people have already done the same thing so I'm sure Google will turn up loads of examples for you to follow. The fact that you're new to Arduino doesn't absolve you from the need to do things for yourself.