Yes, output noise is lower than input because noise passes through the 10 dB attenuator.
Input noise is calculated based on the jjx's suggestion, if I undestood it correctly Ni is calcualated by No/0.1, 0.1 being the linear gain of -10dB attenuation.
If we agree that all other variables are measurable, this brings back my original question, how does one measure/determine the input noise, Ni in the equation to find SNR at the input, to hence find the noise figure . In this example, I am using the formula to find a NF of a 10 dB attenuator, but I can apply it to amplifiers too. I just don't know how to find the input noise Ni.