How to view Center-Aligned PWM on an Oscilloscope
Write some code to flip back and forth on successive PWM cycles between two PWM values, say 10% and 50%. Typically you'd use an interrupt for that. 

If the centers are equally spaced on successive pulses, it's center-aligned. If the spacing alternates between large and small it's edge aligned. 

You can't tell the difference by looking at it outputting a single PWM value, because you usually have no available reference edge to compare it to.