In C mi, it is simply C, E flat, and G. For G7(b9), that is considered a "dominant polychord" So you will use the third and lowered seventh of G, which is B and F. And then you play the major chord of the sixth of G. So basically an E chord with the third and lowered seventh of G. In general, for a G7(b9) The notes are G, F,A flat,B. And if you really wanted to be simple. It's G,B,F just like a G7 with A flat (flat nine) But usually you don't play the A flat and G in the same octave because it's a half step. Same with the G and F because of whole step.
