Allow the stand mixer to kneed the dough for 8-10 minutes. The dough will be ready when it’s smooth and silky and bounces back when you press a finger into it. If you’re not quite sure the dough is ready, you can always turn it out onto a floured surface and kneed it a little by hand. You want the dough to be supple enough to fold and kneed without too much strength. You don’t want the dough to become tough.
If you want to add chocolate chips to your challah, turn it out onto a floured surface and fold in the chocolate chips as you kneed it a few more times. (Sprinkle the chocolate chips on the dough, fold it over, stretch it out, sprinkle more chocolate chips, fold it over again and repeat until you feel your dough has enough chocolate chips spread out in it.)