Recommended translation: "Theaetetus" in The Being of the Beautiful: Plato's Theaetetus, Sophist, and Statesman,  trans. Seth Benardete (University of Chicago Press: 1984).

About the dialogue:

In the Theaetetus, Plato explores the nature of knowledge.

Online:
Amazon (Recommended Translation)
Project Perseus (English, Free Access)
Project Perseus (Greek, Free Access)
Project Gutenberg (English, Free Access)