“How did you find out about this?”

You go to an event for people who are interested in learning and studying English. You introduce yourself to someone and ask them:

How did you find out about this?

find out about (something)

This means to learn about something for the first time. It also carries the sense that you have discovered something that other people might not know about.  If there's a specific idea that you found out, the way to express it is "find out that (clause)":

My wife found out that one of her employees was stealing from her.