This is an exercise I came up with since I have carpal tunnel syndrome and can’t play as much as I’d like to. I either sing along with this mp3 or I do long tones on the root while listening to the track.
The mp3 includes all the modes of Major, Melodic Minor, Harmonic Minor, Harmonic Major, Diminished W.H., Diminished H.W., Whole Tone, Classical Augmented Half Step, Classical Augmented Whole Step.
Of course you can add as many scales and modes as you’d like, but this is a good start. I’ve found that just holding or singing the root while listening to the different modes is very good for the ears and is relaxing as well.
Another option is to sing along with the slower version of the mp3 which is more challenging but even better for ear.