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

If your life is filled with nothing but happiness, every time someone says something to you, all you can do is say, "Sigh, what (さいわ)?" You sigh and say what. Because you're too happy to really listen. You're just sighing all day and not paying attention.