You go to an
event for people who are interested in learning and studying English. You
introduce yourself to someone and ask them this.
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.
This
band is awesome! How did you find out about them?
To share a
specific idea (rather than a general topic) 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.