If you are in an airplane well above ground level, but low enough to see the faces of people relatively easily, and an earthquake happens, will you see the ground shake?
It depends largely on how deep, or shallow, the earthquake is, how large, and what kind of terrain you're looking down on. Some fairly large earthquakes, magnitude 6-7, can have very little surface effect, when they are centred 5+km down as many earthquakes in New Zealand often are. The finer the sediment on the surface, and the thicker the sediment cover, the greater the ground shaking is at the surface and the more motion is usually visible. Different ground covers will also make shaking more or less visible, long grass, or cereal crops, on a windy day will look like they're in motion even without a 'quake.
Shallow earthquakes often result in apparent L-wave activity, by which I mean that you can actually watch the ground wave coming towards you if you're outside on relatively flat ground, even during relatively small 3-4 pointer 'quakes. These waves also make parked vehicles rock from side to side, I would expect these effects to be the most visible from the air in the case of small to moderate earthquakes.
Larger 'quakes will cause noticeable shaking of buildings, power poles, aerials etc... even when quite deep and possibly distortion to large linear features such as roads, railways, waterways, and crop and orchard rows. These distortions would be visible as they form, and, when large enough, from very high in the air.
Whether you would see the ground shake or not depends on the magnitude of the earthquake. If you are talking about the kind of quakes we have in Britain, then no, you wouldn't see anything. Even on the ground you wouldn't see anything, though you might feel the vibrations (I have felt them myself). On the other hand, if you mean the sort of magnitude 7 or 8 earthquakes sometimes experienced in places along the San Andreas fault in California, in Iran, Japan, Indonesia and other parts of the world, you most certainly would see the quake happening from a low flying plane. Sometimes these huge quakes open up great cracks in the earth, stretching for hundreds of metres, roads are severed in a fraction of a second, with the two ends severely misaligned, bridges collapse, the tops of tall buildings sway, and so on.