Which figure of speech is used in this text?
It's an open secret that Brett is writing a book based on his experiences living in Singapore. He never talks about it, but almost all his friends know.

 - euphemism
 - oxymoron
The text uses an oxymoron, a joining of two seemingly contradictory terms.
Open secret is a contradiction, because open describes something that is freely or publicly known, and a secret is hidden.