Which figure of speech is used in this text?
I know that I know nothing.
—attributed to Socrates
A: euphemism
B: paradox
The text uses a paradox, a statement that might at first appear to be contradictory, but that may in fact contain some truth.
I know that I know nothing at first appears to be contradictory: by admitting that you know nothing, you admit that you must know something. However, it contains some truth: it is possible to be conscious of one's limitations.