Scales to Play Over Cdim7
Every chord is a subset of several scales: any scale that contains all of a chord's tones fits over it. Pick a chord to see the matching scales from its own root, the major keys the chord belongs to, and full fretboard diagrams for every scale on guitar.
A Cdim7 chord contains the notes C – Eb – Gb – Bbb. Any scale that includes every one of those 4 tones fits over it — from the root C, that means C Half Whole Diminished, C Whole Half Diminished and C Gypsy Major. They differ only in the notes between the chord tones, and that is where each scale gets its color.
Cdim7 is not diatonic to any major key — it is a chromatic color chord, so treat it as a moment of tension: lean on its chord tones from the scales above, then resolve to the surrounding key when the progression moves on.