I tried deleting and reinstalling but it still doesn't work it would load with sound but just a black screen. It's the only app that does that, not sure what to do.
Well, it's not uncommon for many apps to not work after an iOS update. I'm sure other Fruit Ninja users will chime in. In the meantime, check out the developers website and drop then an email. They may already be aware of the issue and have an update pending Apple approval.
All of Halfbrick's apps don't work on iPhone 6 or iPhone 6 Plus and I emailed the developers. Fun fact: another game "Fish Out Of Water" is completely responsive but you only see the game characters, no environment, no buttons, nothing else. Plain black there.