Are my cookies cooked?
There isn't a universal way to tell. It's going to depend on the type of cookie. For chocolate chip cookies, I watch for a slight amount of browning around the edges. If you're using a chocolate flavored dough, that won't work because the dough is already dark.  So you'd have to watch for changes in the surface, such as cracks or dullness. The bottom line is that you're going to need to read the recipe and then experiment with it until you learn how to get it right.

As a general rule, the cookies will still be very soft and appear slightly underdone when you remove them from the oven. Leave them on the baking sheet for at least five minutes before transferring to a cooling rack. They'll set up during this time due to residual heat.