This is a jukugo word, which usually means on'yomi readings from the kanji. Since 人 has two on'yomi readings, here's a mnemonic to help you remember which one to use:
Imagine a black person you know well wearing coke jeans (こくじん). Yep, jeans made entirely from coke bottles. That's actually a thing. Look it up if you don't believe me.
I can’t understand how there are still people who discriminate against black people.
I'm black, he's white. What's wrong with that?
Peanut butter was invented by a black person named George Washington Carver.