14.50Improvisation over a passing diminished chord

Suppose:

C | C♯°7 | Dm7

Do not immediately search for a complicated scale.

Start with the actual chord tones:

C♯°7:

C♯ E G B♭

And resolve them:

C♯ → D

E → F

G → A

B♭ → A or C

Those resolutions practically write the improvised line for you.