Money
Wealthy would be that you are rich and don't care about anything but your money and you. Knowledge would be that you know and/or care to learn things. The difference between them is...
Knowledge is such a wealth which can't be stolen, Monetary wealth is being protected whereas knowledge protects. Wealth may perish but knowledge of wealth can never perish.
You can use both. You can use "knowledge of" when you are saying that you have the knowledge of something specific. You can use "knowledge in" when you're talking about a vast area/field of...