For games it may be Unity, the Unreal engine and the like. To know them is a much better qualification than to know how to set up some OpenGL shaders.
I don't completely agree to this. When I started game development, I jumped straight into Unity. I did that because it was simple (or at least I thought so) and everybody else used it.
I soon discovered that it wasn't something for me because I didn't understand a thing. So then I jumped over to Java and LWJGL; making small steps every day. And now, about three quarter of a year later I've made a pretty neat game engine (in my opinion), and best of all: I've learned a ton.
I also recently picked up Unity again, just to see. And guess what? Almost everything made perfect sense, and it didn't take me long before I made a basic prototype.
So I think that it's a combination of them both; it will make your day easier if you know some of the underlying mechanics (or have some serious experience).