2. Do I need specific app to use the Q1II with iPhone?

A: No, you don't. You don't need any specific app to use with iPhone. However, if you wanna play DSD files, you would need a player that could support DSD playback. 
We  have the FiiO Music app (for iOS) that could support DSD playback on Apple's App Store. You're welcome to test it at the time.