The Cm6(9) respectively Cm6/9 is a minor 6th chord with an additional 9th and therefor consists of the tones C (1), Eb (m3), G (5), A (6) and D (9). The 5th can be omitted.
The notably jazzy sounding m6(9) chord can be applied as known from the m6 chord. It sounds especially good when the previous chord also has a 9th, like for example Cm7(9) Cm6(9) Bbmaj7 that you may play instead of the basic II-V-I progression Cm7 F7 Bbmaj7. The Cm6(9) chord contains the same tones as a F13 chord without the root F, no matter whether you play or omit the 5th of the Cm6(9): Cm6(9) incl. 5th = F7(9,13) without F Cm6(9) excl. 5th = F7(13) without F
The m6(9) chord is commonly written as m6/9, but it's not a slash chord!