The Cm(add9) chord is a minor chord with an additional 9th, but without a 7th (which would be inluded in the Cm9 chord). The Cm(add9) chord consists of the tones C (1), Eb (m3), G (5) and D (9).
The tone D is written as 9 and not 2, because 9 is a chord extension, while 2 means a modification of the base chord and only exists as sus2 that would replace the 3rd.
Unlike major chords, that are dramatically changed by adding a 7th, minor chords can in most styles be played with a 7th even if it just a plain minor chord is written. Or the other way round: played without a 7th, although the chord symbol says m7. Conclusion: m(add9) chords are mosty a result of playing a m9 chord in a way that doesn’t leave space for a 7th on the guitars fretboard. In most cases you should prefer writing a Cm9 chord on your music sheet and then just play it with or without the 7th depending on your chord shape respectively voicing (order of intervals).