It's easy to recognize the cogni-
in cognizable and in other English words that have to do with knowing:
cognitive, incognito, precognition, and recognition, for example. They're all
from Latin cognōscere ("to get to know" or "to acquire knowledge
of"). Cognizable was formed in the 17th century from the root of
cognizance, which in English means "knowledge" or
"awareness." Cognizance traces to cognōscere via Anglo-French
conoisance and conoissant, meaning "aware" or "mindful."
Cognizable was used in its legal sense almost from its introduction, and that
meaning continues to be most common today.