This is a specialized word for specialized situations and is used most of all in the world of business, when someone is describing what they do that makes them unique in the marketplace. If you can find a product or service that you can perform better than anyone else, and you can make your living from it, then you'll have found your niche in the market. When you do, you'll probably want to get the pronunciation correct.
There are men and women who sit on the boards of Fortune 500 companies and talk about finding their next "nitch", and they better hope their ideas are better than their pronunciation, because that's wrong. The soft 'c' means they should really be looking for their "neesh". Now that we've cleared that up, feel free to use it at your next job interview.