I have Mac OS Sierra. Unfortunately, I cannot upload my app due to a bug in Xcode 7.3.1 that makes it impossible to upload to iTunes Connect from Mac OS Sierra.
I have found a work around: Can I upload Xcode builds on macOS 10.12
However, it says I need to find my app's "archive" file. I believe that is the same thing as my app's .ipa file.
Where would my app's .ipa file be located?
They are stored here:
~/Library/Developer/Xcode/Archives
In that folder you will find a bunch of folders by date.
Alternatively, open XCode, go to Window
-> Organizer
. Right-click the archive you are looking for and select "Show in Finder"