Nose for News is actually a unique ability of a journalist. This is related to the idea of newsworthiness. Not every single event is worth being news. This is why we try to ignore events with less importance, or in other words, lacking newsworthiness. But a journalist must possess the ability to find out an extraordinary story within a number of ordinary stories. A journalist must have a keen skill of sensing such news stories. Dogs (and some other creatures) can smell things from far away which many other animals cannot, and it is believed that they can even smell (sense) 'omens' sometimes (i.e. of natural disasters) beforehand. The comparison, in essence, is made to indicate that very quality of a journalist to finding out an extraordinary story hidden within ordinary day-to-day stories.