The dough will look smooth and shiny, feel soft and springy, and will pass the windowpane test. Tear off a piece of dough and stretch it between your fingers. If it tears, it fails. If it stretches and forms a translucent rectangle, it’s ready to shape into a loaf for proofing or baking.
It’s hard to over-knead dough by hand, but easy to do so by machine. Over-kneaded dough will be dense and rip easily, baking into a dense and flat loaf. If over-kneaded, you’ll want to start over.