As many of the other reviews at Glassdoor have pointed out, there is a phone interview followed by onsite. Unfortunately, I can't disclose any coding questions due to NDA however they are all from Leetcode tagged under LinkedIn.
Here was the structure of my interviews:
Phone Interview (1 hour)
I was asked some basic iOS questions and 2 questions (one medium and one easy) from Leetcode and we used Collabedit (or some other code editor I think dont remember) to code and verify that the algorithm works. The interviewer was happy and a couple of days later, I got an invitation to schedule for onsite interview.
Onsite Interview
Two weeks later, I was on onsite. The interviewers were all really pleasant and fun. I had a total of 5 rounds of interview (including the lunch with one of the employees). Here was my ordering of the different rounds but keep in mind that they can be in any order:
1st Round (iOS Specific coding)
This round is fairly straightforward and you're asked to build a very simple app (which consists of a couple of screens at most). Just make sure you know the basics of parsing, and building UI (storyboards or programmatically anything is fine).
2nd Round (Chat with a Manager)
This round is the behavioral round where the manager asks the standard questions, "Why do you want to work at LinkedIn...etc...etc" and also introduces himself and some of the projects he/she is working on. The manager also asked a brief design question of how you would design a particular feature on the LinkedIn app, but this was just conversational, not whiteboarding or anything like that.
3rd Round (Lunch with employee)
This round is really fun as you get to taste some food of LinkedIn :D and also chat with the employee. So somewhat relaxing but keep in mind that even though this is lunch, the employee is still evaluating you, so keep it friendly and make sure the employee is engaged.
4th Round (System and Design Question)
This was a mobile architecture question which deals with designing a suitable API for the client and the interactions with it. Not that difficult, just make sure to explain the API structure you choose and also make sure to explain the front-end structure (how you would structure your classes, models, views, controllers, etc)...
5th Round (Algorithms and Data Structures)
This is the round where luck can play a huge role (in my opinion of course). However, I got hopelessly DESTROYED :( Dynamic programming was my weakest link and I got asked a difficult Dynamic Programming question (similar to longest palindromic substring). I couldn't figure out the solution in the given 45-50 mins so I got wrecked. Oh well.... :(
Even though (I thought) I did really well on the other rounds, received a rejection a week later but was a positive experience nevertheless and would definitely want to interview again if given a chance in the future.