One place I worked at, the company hired a developer who claimed to have a CompSci masters.
He was completely unable to code anything. I thought it strange.
I started to ask him some basic questions that any actual CompSci degree holder should be able to answer (and I don't have a degree in CompSci at all - everything I know I've learned on my own, from other sources, for the most part); I didn't make it like a grilling session, just polite conversation about a shared interest - but he either had difficulty, or couldn't answer at all.
He only stuck around a couple of weeks.
I've often joked that an interview question should be asked akin to "What basic logic function is needed to implement a computer? Show it's truth table, then design one in 2-dimensions on a whiteboard as a virtual 'rope-and-pulley' system."
Couple that with a random-style fizzbuzz-like challenge, and maybe a more difficult open-ended programming challenge (ie "build a simple CRUD app") - that would give you a good idea on their real skills.
Note: That first question I wouldn't expect many to be able to pass the last part; even the first two parts many perfectly capable developers would have difficulty with. But I would be disappointed if they claimed to have a CS degree and weren't able to at least tell me what it was and the truth table for it.
I should note that my statements below may be FOC; I do not myself have a CS or EE degree, so take what I say with a modicum of salt...
But first, note that I wrote "function", not "circuit".
It could be argued that CS, on the whole, is a subset of mathematics, particularly that of boolean algebra and logic. As such, the functional equivalency between the abstract of boolean logic/algebra, and its implementation on a physical substrate, could be considered among the most important of CS concepts.
One could also argue (maybe?) that Turing's "equivalency theorem" might be related to such as well. Consider the case of an emulation of hardware done in software; one could consider that - at a base level, it is boolean logic expressed physically, being expressed equivalently as boolean software functions.
The opposite it also true, of course - that it is possible to express software boolean functionality in the equivalent physical form.
What form it physically takes does not matter (other than speed of course), which is why I also didn't ask for an implementation/representation in electrical terms or schematic form, but rather a diagram of something that could be expressed as a physical and mechanical object. If the person were so inclined, they could express it as a series of levers and marbles, or in LEGO, or Meccano, or any other similar option.
EE knowledge is not needed here, I don't believe (Martin Gardner might agree).
did you talk like this to the CS masters, no wonder they left