In an interview you're going to get asked many different programming questions and to take a programming test.
Topics include things like:
How to Implement a binary search for a set of sorted numbers.
Write your own function to insert a node into a linked list.
Write a function to sort a linked list.
Write a function to reverse a linked list.
How would you design and code a Poker game, or a chess game, or some other simple and known game.
What is wrong with this code? Debug a problem, or find a problem.
The STL if the job is C++.
Explain different programming concepts / definitions like:
What is the heap, what is the stack?
What is polymorphism?
Describe a polymorphic relationship.
What does new and malloc do?
What is virtual?
What is the difference between a class and structure?
What is encapsulation?
Explain managed vs unmanaged.
What's a copy constructor, move constructor, destructor, when are they called.
Whats a friend?
What does it mean to be pure virtual, what is an abstract class?
What is abstraction?
What are namespaces?
Most game companies may also ask you questions to gauge how well you know your linear algebra, trigonometry, bit manipulation, and/or physics and how to apply them to a game. So make sure you know Dot Product, Cross Product, Matrix math and how it's used in games. This is especially important if you're looking to do graphics work.