Confirm where examiners may be busy (6)
I believe the answer is:
attest
'confirm' is the definition.
(to attest to something is to prove or confirm it)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for attest that I've seen before include "Provide proof of, declare to be true (6)" , "say, in court" , "Declare to be true or genuine" , "show?" , "Declare (that something is the case)" .)