How to do market research on audiences?

Hey guys, in a few months, I will be 18. For now, I'm watching a dropshipping course, and I want to focus on finding a winning product and a winning audience. I think the second one is the most important. However, I sincerely don't know how to find information about a specific audience to see how they talk, what they like, what they dislike, etc. I saw in a copywriting course that I should look into YouTube comments, but there isn't much useful information there.