Presumably you'll be asked things such as the ports used by well known services, such as DNS, SMTP etc. and basic networking concepts such as "how many hosts are there in a /20 subnet?". I expect you'll quizzed on your troubleshooting skills by going through scenarios such as "you can ping a server by it's IP address but not it's FQDN, what steps do you take to resolve this issue?". There may also be novelty questions, something along the lines of "in the event of a zombie apocalypse, where is the best place to find a weapon in an office environment?". These questions are ostensibly to gauge your problem solving skills, but in reality they're a test to see if you're a violent sociopath.
Good luck, and bon appétit!