There is no such point (or it is everywhere if you like, as someone else had said).
The best analogy I've seen is that of ants on a balloon. They live in what appears to them to be a two dimensional universe. As you inflate the balloon, they observe their own universe getting bigger. But the "point where the Big Bang happened" to them is not a point that even exists in their universe any more. They cannot get back there, since the higher third dimension does not exist in their universe.
This illustrates the confusion that occurs when people are exposed to horrible "artistic renderings" of the Big Bang as a huge explosion that throws matter all over the place.
It's better to think of the Big Bang as an unimaginably intense period of expansion and cooling of whatever substance the earliest universe was made out of (see Inflation theory). It was not an explosion that happened in a pre-existing spacetime.
