Make sure that you are candling down into the egg from the top (rounded fat end) of the egg. When the light shines through the air cell you should be able to clearly make out the difference. Candling from the bottom or side will not usually give you a clear picture of the air cell. If your light isn't bright enough or you are candling darker eggs that will also make it harder to see.
If it moves down the egg when you tilt it, like a free floating bubble, it's detached. If it stays at the top but is jiggly, it's just wobbly. Wobbly cells will usually firm up and be ok, especially if they are just tilted instead of rolled or auto turned the first few days. Detached air cells are a pain and there's not much you can do other than hatch upright and hope for the best.
