You can pierce through the layers of your designs to see the specs of each one of them. To do so, just click repeatedly on the same spot until you get to the layer you need.

You can also navigate using our layers menu located in the menu at the left of the screen. 

Both methods are particularly helpful with Sketch symbols. Since symbols are just groups of layers there's no way to exactly know what specs of layers to show when clicking on a symbol. With this you can pierce through the layers and see all the specs of your symbol.