The statement "if there is one thing I know it is that I know nothing" is best described as a paradox.
A paradox is a statement that seems contradictory or self-defeating but may actually reveal a deeper truth. In this case, the speaker asserts that they know nothing, which contradicts the idea that they "know" this one thing. This juxtaposition creates a thought-provoking contradiction, typical of a paradox.
On the other hand, a hyperbole involves exaggerated statements not meant to be taken literally for emphasis or effect. Since this statement isn’t an exaggeration but rather a reflective contradiction, it does not qualify as a hyperbole.