You don't need to know everything about operating systems, but there are some commonly asked questions that you should know how to answer
Much like SQL, there is too much things to cover when talking about operating systems and most importantly, concurrency patterns. I have attached my notes from the operating systems module in NUS (CS2106) for you to self-study
Classical concurrency problems
Some of the other commonly asked questions include things like:
What is a deadlock?
What is a race condition?
What is the difference between deadlocks and race conditions?