consider that I work for blue chips and I assist in recruiting production DBA's. The roles always ask for performance tuning and diagnostic skills, if you don't know what a bookmark lookup is or if a PK can be clustered or not then you will certainly not get hired. As I say I don't ask about syntax of dbcc but I might expect a dba to know how to extract cpu/worker thread information , if not the exact commands where it can be, likewise if the value of page life expectancy should be high or low ( another good question many get wrong).

However if a candidate writes in their cv that they tuned the disk subsystem to improve performance then they better sure as hell know about random and sequential io, throughput , spindles and raid performance. I'd expect any dba to know the difference between raid 0, 10 and 5.

The fact that the product is so good, SQL Server, is perhaps the reason that to a certain extent the quality of some dba candidates is disappointing.

btw the reasoning behind the PK question is that if you've only ever used the GUI to manage and work with SQL Server then you'd not know you can create a non clustered PK.