How Do I Know A Person's Whereabouts Through Their Mobile Phone Number?

If you mean country province or state wise look up the country code example 1-604-533-5655 1 would determine the country in this case canada, 604 determines the region in this case the bc coast, and 533 is generally a langley number. These things either need to be looked up online or asked of someone in that area haha. If you mean how to use a phone number to track exact location like gps, the iphone has an app for that