Conducting technical interview is an art.

Most likely I would start a discussion with simple questions like "What is your favourite topic in SQL Server?" .

here are some open ended questions that could be answered in 10 seconds or may lead to an hour long interesting discussion.

1. I have created a Non Clustered Index to improve a query performance.
But Optimizer did not use it. What could the possible reason?

2. If you are given only 10 minutes to find root cause of performance issue in SQL Server 2008 Instance, what you would do?

3. Someone has deleted a record in a critical table. Can you find who deleted that record?
Is it possible to get back that record from t-log or backups without restoring the database?

4. How many locks are required to update one row in a table?

5. What are the system pages available in a data file?

6. What happens when SQL Server service is started?

7. What happens when a CHECKPOINT is issued?

8. What happens when an user execute a simple SELECT statement?

9. Is it required to enable AWE on 64 bit servers? why?

10. What you will do if a production database is corrupted?

11. Under what scenarios do page split occur? (DELETE?)

This not necessarily be suitable for all developer and DBA interviews. but I would ask similar questions if the person claims that he is storng in
Internals and Performance tuning

If any of your open question leaded to healthy long interesting discussion, please do share with me.