Don’t need a certificate. Go do it on your own, business school teaches you this stuff but I saw from my dad that he learned it on his own completely. Go to investopedia.com to learn about the vocabulary. For college, they don’t teach you ONLY this stuff. You have to take a lot of other courses so you can’t exactly focus on just stocks. Mutual funds and bonds are involved too. All of this is called “investing” lol.

Stock brokers might let you intern with them if you show them that you know something.

First off, your question is stupid. One does not learn to trade stocks at college as the process is quite simple. Rather one gets an education in how markets function and react to different situations. This degree would be economics. The other being the role of money in markets. That would be finance.

Economics and/or finance would be your best bet to understand the market and for being a broker. Just because you have an education in either of those does not automatically make you a good broker.