You can get Stockfish app and Play The Opening Against him. I haven't found an Opening-centric Good app yet.
iPad apps opening training

An ipad app called, chess openings lite.
https://itunes.apple.com/us/app/chess-openings-explorer/id414945089?mt=8
Amazingly huge library, no need to go to the pro version. I swear by this app.
If used in conjunction with stockfish even better!
Anyone know or can recomend an ipad app for learning openings?