Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:

You want to compose a poem but all you have for inspiration is what's in your pocket. You reach in and find a yo-yo (よ). Ah yes, this will do. So you compose a poem about your yo-yo:

One string to rule them all,
One string to find them,
One string to- hey wait a minute...