What kind of position are you thinking of applying for? If your going programming you want to be able to show off your problem solving and software engineering skills more than a pretty demo (not saying that a pretty demo doesn’t help, just remember it is possible to write crappy code and yet have a wonderfully polished looking demo).
If you are going for graphics programming, I’d guess you need to demonstrate knowledge of computer graphics theory (rasterization, colour theory, spatial partitioning, raytracing etc). I reckon that would be more important than know a grahpics engine or libary off by heart.
If you are going for AI, maybe write a good demo which shows you know how to use common AI techniques such as flocking/steering behaviours, pathfinding or FSMs. Simple graphics would work fine for something like this.