。
She knows the trick to making money.
Literal
She [topic-は] money-making [genitive-の] knack [object-を] is-knowing.
こつ ('knack, trick, the key to') is one of those tiny, useful Japanese words — written in hiragana more often than in its kanji 骨 (which means 'bone' but here metaphorically 'the bones of the matter'). Phrases like ~のこつをつかむ ('grasp the knack of'), ~のこつを覚える ('learn the trick of'), and ~のこつを教える ('teach the technique of') all use it. Implicit here is positive evaluation — she has acumen, not just luck.