How to retrieve 3D camera angle of rotation along Z-axis

If I am using the 3D camera, how do I check or have the system return the value of angle of rotation for 3Dcamera along the Z-axis, say, for instance if the player/camera is tilting or looking downward or upward, how do I get the angle of tilt (value in degrees) for the camera?

How are you setting it in the first place? Save that value to a variable somewhere.