Upon installation of the KronosRemote iPad app from the Apple app store you agree to Apples terms and conditions. This might include storage of personal data related to your Apple products and bought items.
The KronosRemote app itself collects instrument-related data from your Kronos keyboard like preset names and settings. These data are stored locally on your iPad and will all be deleted when you deinstall the KronosRemote app.
In case you import .pdf documents or .jpg images to be displayed in setlist mode, these documents are stored locally on your iPad as well. .pdf and .jpg files can be managed (imported, deleted) using the Apple Files app or the KronosRemote app itself, if you delete your data here there will be no more local copy. Also these documents will be deleted when you deinstall the KronosRemote app.