Whether you say Niche like “NICH” or “NEESH”, you are correct. As you can hear in the video below by Oxford Dictionaries, NICH is the American English way to pronounce niche. British English uses both NICH and NEESH.
Most dictionaries actually show both as correct. I personally say NICH where most YouTubers these days seem to prefer neesh. In either case, you are correct.
The french pronunciation is NEESH.
Definition according to Webster: : a place, employment, status, or activity for which a person or thing is best fitted [Hear it pronounced]