How deep should an iOS developer review data structure & algorithm when preparing for iOS job interview position? I know most people would just say there's no harm in reviewing it, but would like to get some insights based on your experience interview what are the percentage of the questions are related to data structure/algorithm and what percentage are iOS related?
I would suggest you don't need to know that stuff: iOS includes a Foundation library where people have already solved those problems. I've only worked on one app where I needed to augment the data structures provided by Foundation, and in that case I was specifically working as a performance engineer.
The general case for an iOS developer interview is that you need to know Objective-C including memory management, you need to know the UIKit and Foundation APIs, and you need to know how to communicate efficiently with a server-side component.
If it's a larger company, at least one person on the interview team may be assigned to make sure you can program your way out of a paper bag. It's a big red flag if you can't talk your way though simple programming problems (which may involve some knowledge of common algorithms and data structures), no matter what's on your resume and/or portfolio.
If it's a very small company, they likely just want you to show them your finished working iPhone apps, and show that you know enough to write more like them.