Perfect Pitch Trainer is the perfect app to learn to identify piano notes.
Generate and identify music notes until your heart's content. You will be able to press an onscreen keyboard to identify what note is being played.
You will be able see stats on your performance including how accurate you are at identifying each note, and how long it takes you to identify each note.
By default there will be 5 octaves that a note could be generated from, but there is an option to enable only 1 octave to generate a note from, which will be handy for beginners.