Phonak Audeo Infinio I90 Settings

It can be saved on both.
You can read the settings from your device and save them to Target.
If the settings in Target are different than the ones stored on the device, the software will ask you which one you want to load when connecting the device .
When you are done and you are ready to save the session , it will ask you if you want to save the changed settings on the device or just the software (or both).

How about the audiogram?

Yes , the audiogram too
The only thing that is not stored is your personal data from what I remember (name , age , etc )