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:
Something is lacking... it's a car (か). You can't stop thinking about this because you have to walk 40 miles to get to your destination. If only that car wasn't missing, this would be easier. Imagine the sweat... the pain... the thirst... all because that car's not present.
I fell off my bike and chipped my front teeth.
That plan is lacking in reliability.
I lack the willpower to stop watching Sailor Moon.