Before we answer that, we would like to highlight that Apple prefers iOS development with standardized languages, frameworks & architecture. That’s why Swift (a proprietary language made by Apple) is the key programming language that our developers work on.
Now coming back to the technologies, with TBI you can hire iPhone app developers who can work on the following technologies and tools proficiently:
Swift, Objective-C & iOS SDK
UIKit, CoreData, & APNS
GeoLocation Service & Networking,
GIT version control system
OOP and SOLID principles.