Objective-C and/or Swift
Cocoa Touch
iOS frameworks (Core Data, Core Animation)
Design Patterns (MVC, Singleton)
Offline storage, threading, performance tuning
RESTful APIs
3rd Party API integrations
UI/UX standards
Apple’s design principles
Low-level C-based libraries
Performance and memory tuning tools
Cloud message APIs and push notifications
Benchmarking and optimization
Code versioning tools (Git, Mercurial or SVN)
Continuous integration