Was there a feature in Cubase 8 to analyze a midi clip I wrote and tell me the key or chords I wrote? I seem to remember hearing about such a feature,
In the Key Editor Inspector’s Chord tab near the bottom is a button to “Create chord symbols” which will look at the part you have and put chords onto the Chord Track. There are several options in the dialog that opens. Then you can have Cubase decide what key or keys the chords are using. The results may or may not be satisfactory - but at a minimum it is a starting point.