Information

Then, what should test our candidates ?

For sure it is their understanding of important principles, and, preferably, how they adapt to actual needs and constraints - which is a good indicator on how well they understand the principle. After all, this is the capability we expect for specialists. They are no primary school students and should not earn their salt by their short-term memory (which inevitably would decline with age) and being able to recite textbooks.

As TS Eliot said:

What's the wisdom we lost in knowledge ?
What's the knowledge we lost in information ?

Well, Eliot is too much for many with tunnel vision (a sign of papilloedema as a result of too much stuff in their head), I know.

PS. In our case of brain-stem death, for example, it would be more appropriate to ask what the candidate would do if the patient has a skull or neck fracture so that some of the cranial nerve test could not be performed, or what to do if one of the tests does turn out to be reactive !