Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word: You take your cloth and put it on top of your head. It's there because right at noon (ぬの) the sun is in the middle of the sky and burns your scalp. So, you cover it with a cloth. Imagine yourself setting an alarm for noon to help you to focus on the noon part.