Check out links on this website about how to candle eggs, or follow YouTube, there's a few on there. Using a flashlight there is a way to see inside the shell without causing harm to any developing embryos.
Quail eggs can be difficult to candle, so the brighter your light, the better. High lumens, like 250 or more. Look for darkness and blood vessels. Shine down thru the air cell end of the egg.