In Xcode’s Organiser, go to your device’s Summary tab. Find your application in the list, and click the disclosure triangle. Under it, you should see an icon saying “Application Data”. Click the down pointing arrow to download the data, and it’ll prompt you for somewhere to save it.
In Xcode 5, listed under your device in Organizer, click on “Applications” and you can see “Data files in Sandbox” in the bottom half of the window.
In Xcode 6, go to Window -> Devices, select the device, select the app name under Installed Apps, click the settings gearbox, then select Download container…. In finder, double finger tap the package and select Show package contents.
