Yesterday, I met a beautiful woman of unknown age.
Wanikani is a monster whose sex is unknown.
His real job is unknown, isn’t it?
Something is not detailed at all. I don't know anything about it. No details whatsoever. It's a totally unknown entity. It's unidentified.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.