I get what you are saying, and no one knows everything. But, there are basics that everyone kind of should know.
What a vlan is, how it works, why we use them, how arp works, what NAT is, different types and why we use it etc
For security it is kind of the same. I would expect people to know what stateful inspection is, how a state table looks, what anti spoofing / uRPF is, basic idea of PKI, some AD knowledge.
What I do when going through a C.V. is look at what the person has put there, and ask them questions on that. So if they say,
experience in firewalls and VPN's.
I would ask firewall questions, starting from basic and working my way up. If you say you are excellent at firewalls, I expect you to know the hardware architecture of the security devices, how the integrated UTM sections function and what kind of architecture they use etc etc. For vpn's, if you say you are strong on them, I would ask questions like, what is the point of doing a DH exchange? What is the password used for in the VPN? What benefits does IKE v2 and why would you use aggressive mode negotiation
But even in an interview, its pretty easy in the first 2 minutes to see if the guy has potential or not, and if he has the core knowledge or not. Some guys we have hired and flat out said "i have no clue how that works" to lots of the questions, but the questions that are in their field, they know down to the nuts and bolts. That shows they truly take an interest in their job, and most likely just havent had the exposure to other elements.