When do I add the Chocolate? Chopped and thrown in the batter? There isn’t anything written in the recipe about the chocolate

I agree on adding the chocolate to the dry ingredients, but doubt adding after the egg whites would work.
As my second method, I suggest scattering the chocolate on the bottom of the pan, then pouring on the completed batter. When baked and inverted, the chocolate will be scattered on top if the cake, with some for every slice.
Either way, roughly chop the chocolate before adding.