How to find apps registered to a different iTunes account An acquaintance of mine bought a used iPhone. The previous owner was a  friend. They installed some apps that the new owner wanted, but used the previous owner's iTunes account for convenience.

Now she has a new Macbook and wants to connect the iPhone to the iTunes running on it.

iTunes, however, refuses to do so before getting authorization for 10 apps that were registered using the former friend's account. This is what the dialog looks like (in German, sorry):



the friend is no longer a friend, so there is no way to get their password for the authorization. iTunes won't tell me which the 10 apps are.

I have no problem with just removing the 10 apps and reinstalling them, but I'm scared that they'll contain important data (like her Whatsapp which is chock full with contacts and chats).

Is there a way to tell which 10 apps are connected to the previous owner's account?
You can go into iTunes on a computer and go into her account. From there you can look at all past purchases (also includes free apps) made with that account. 

Find the apps that are on the device but not in her account. Those will be the apps from the previous owner.