I am going to interview onsite for these companies. I have 3 years iOS experience. What should I expect in terms of the iOS domain specific questions? Also, how does an iOS system design interview look like?
It's pretty standardized these days. I felt pretty similar vibes from the 6-8 phone interviews I've gone through recently. I had on-sites with FB, Uber, and Apple.. Know iOS memory management Know Xcode Instruments and when to use them Know UITableView and UICollectionView + data structures and your data sources Pros/Cons of Delegation, NSNotification, KVO Design: "Twitter feed", "IG feed", "list -> detail view", etc. Separation of concerns, modularization, protocols, explicit types and initialization of classes, how are certain classes referenced by others? Start simple, always be talking and looking for acceptance before continuing. Try not to explain something beyond your understanding. At a few years of experience, it's more dangerous to try reach to far in your explanations of best-practices, patterns, etc..
Glassdoor can help you with the FB iOS onsite experience. Not sure about others though.