Considering you can't really get accredited or certification for search engine optimization you have to know your stuff prior to any interviews with a company. Really, if you can't do any of the optimization work without asking someone else a question here or on another forum you shouldn't be taking the job.
Rand over at SEOmoz made a great video the other day called How to get an SEO Job. Watch that, he brings up some good points that will help.
The SEOmoz video is really useful, but the comments for the post are good too. Make sure you read them.
The important matter about the SEO world is having logical answers to most of the questions raised. You know, the whole search engine optimization is to find answers to the ranking questions.
When you attend any other interview the background knowledge of the subject is very important similarly for SEO Experts Interview you shoud have some knowledge. If you are unsure what is seo, learn by searching here
You need to concentrate on what the question is being asked, and limited to that only portion of the question, do not redirect to another point which is not relevant to question,