If a person applies for several jobs through several sources say newspaper, websites and other means and so while attending interview he could not source the way through which he or she has applied for the job but was put a question on that how must one present the answer for facing this scenario.

I feel that there is nothing wrong in admitting that you could not remember the source of job and you could also add by saying that you normally apply through what all modes and may be it is in one the modes.

I agree. I have an IT recruitment company in New Zealand, and I can't tell you how many candidates sheepishly admit they can't remember which job they applied for with us. I'm never offended. When it comes to finding a job (and let's face it we've all been there) we source potential roles from all over the place, so it's hard to remember which one is which.