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 have your bow and you use it to shoot things, sure, but you've also covered it in candy so you can eat it when you're waiting out in the woods waiting for a buck to come by. You lick your candy bow and say: "yummy!" (ゆみ). Imagine the taste of your bow. What taste would make you say yummy?