learn knowledge ×

gain/acquire knowledge √ (but old fashioned)

and "knowledge" itself is gaining a bit of a negative reputation. It's referring to people who know a lot stuff but can't do anything with it, or don't really understand it deeply.

Some alternatives:

I'm going to study economics, because

I want to learn more about finance.

I want to develop an understanding of finance.

I want to deepen my understanding of finance.

I want to gain insight into finance.

When I lived in China, I gained insight into Chinese culture.