The selection of an adept iOS app developer can often be a labyrinthine process, a chess game, if you will, where your next move could instigate the beginning of a successful endeavour or set up a chain of catastrophes. It is paramount to incorporate a set of critical inquiries to the potential developers to ascertain their competency, ensuring the selection of the perfect fit for your project. The objective of this discourse is to delve into the sophisticated realm of these queries, shedding light on their relevance and necessity.

To begin, one of the foremost queries that must be posed to the potential iOS app developer is their level of proficiency in Swift, the programming language for iOS app development. Swift, fashioned by Apple Inc., is the lingua franca for developing iOS applications. It is an integral criterion as it directly pertains to the developer's capability to create a functional, efficient, and user-friendly app.

While questioning their expertise in Swift, it would be remiss not to inquire about their familiarity with Objective-C. Objective-C is the mother tongue, so to speak, of iOS development, preceding Swift. Although Swift is the more contemporary and preferred language, understanding Objective-C can provide a broader comprehension of the iOS environment. A developer proficient in both will have a nuanced understanding of iOS development, akin to a scholar conversant in both Old and Middle English, able to appreciate the trajectory, evolution, and depth of the language of iOS development.

Once the developer's linguistic proficiency is established, it is then essential to broach their understanding of Apple's Human Interface Guidelines (HIG). The HIG is a set of design principles and patterns provided by Apple to offer a cohesive user experience across its ecosystem. Comprehension of HIG will ensure that your app blends seamlessly into the iOS environment, evoking a sense of familiarity and ease in the user, much like how an architect would adhere to local architectural styles to create a building in harmony with its surroundings.

Shifting the focus from the developer's technical know-how, the next area of inquiry should be their experience and portfolio. This will provide a tangible demonstration of their skills and capabilities. Additionally, it is essential to request references from their past clients, functioning as a background check. Comparable to a historian scrutinizing primary sources for a comprehensive understanding of the past, examining a developer's portfolio can reveal their practical abilities, while client references can provide insights into their work ethic, reliability, and professionalism.

Another facet of iOS app development where inquisitiveness is required is the developer's proficiency in utilizing Apple's Xcode IDE. Xcode is the integrated development environment (IDE) used for creating apps for all Apple platforms, including iOS. Familiarity with Xcode is as crucial as a chef knowing his way around a kitchen – it's where all the ingredients (code) come together to create the final product (the app).

Finally, the inquiry should extend to the developer's understanding of Core Data, Apple's framework for managing and persisting data. An adept iOS developer should be conversant in managing data effectively to ensure your app runs smoothly, just as a librarian would efficiently organize books to ensure easy accessibility for readers.

In conclusion, hiring an iOS developer is a complex process requiring a keen eye for technical skillsets, comprehensive understanding, and experience. By asking the aforementioned questions, you could significantly increase the odds of securing a developer who can turn your vision into a successful iOS app. The ideal iOS app developer should be a polyglot in programming languages, an architect of user interfaces, a historian of their own past work, a chef in the Xcode kitchen, and a librarian of your app data. The journey to find such a developer is fraught with difficulty, but with the right questions in hand, you can navigate the labyrinth and ensure your project's success.