How can I download ipa file from ipad on El Capitan? Unfortunately Stash got removed from the iOS App Store, but I need to transfer it from my iPad onto my new iPhone. How can I do that? If I'm right first I need to download it and install it with iFunBox. Where does the iTunes store the ipa files when I do a manually backup?

PS: I tried to restore phone from iCloud backup, it tries to download it but it stuck on "Waiting.." status. The most important thing for me is the data in the app. I tried to contact the developer but I got an automatic reply.
Sync your iPad with iTunes, which will download all not already downloaded Apps to iTunes - and then sync your iPhone with iTunes - that's it. 

iTunes store the ipa-files in ~/Music/iTunes/iTunes Media/Mobile Applications