I don't know what features and functions Cubase has, but if it doesn't have a FFT frequency analysis function then you can use a VST plugin such as
Voxengo SPAN to find the dominant frequencies in the sound. (I'm not saying that's the best plugin to use for this; it was just the first one that came up when I searched for "free vst plugin to do fft frequency analysis.")
The problem is, a single note can (and often does) have more than one prominent frequency, depending on the timbre of the instrument-- or the shape of the sound wave being used if the instrument happens to be a synthesizer-- so you can't always tell from a frequency analysis whether the sound was created by playing a single note or two notes, three notes, etc.