Keyword Research and SEO are entire industries today. There are tools like ahrefs and semrush that promise to give you "trending" topic keywords for a sum of monthly subscription money.

However, you can discard all their claims using a similar logic that you use to discard the claims of Astrologers, Voodooists, Stock Experts who "recommend" stocks, etc:

1. If an Astrologer knows the future of everyone, wouldn't they profit massively from it themselves using the information rather than telling the trick to everyone else (just for a pittance)?
2. If a Stock Expert knew that a stock's price will go up (and how much), won't they invest thousands and make millions themselves instead of giving those "tips" to "subscribers" and again, earn only a pittance?
3. If SEO and Search Marketing companies knew exactly which keywords can rank your blog or site in the Google Search Engine, won't they write articles on those topics/keywords themselves and profit massively with the page views instead of revealing that secret to you for merely a few cents!