Hi
pesik, the procedure to identify the subject in this sentence is actually
no different from the procedure to identify the subject in any other sentence.
Since subject is the
doer of the verb, we need to find the
doer of the verb (in this case doer of verb
is/are).
Hence, to find the doer, we ask the question:
What is/are debatable?
The answer:
Whether brick-and-mortar bank locations will survive this era of online payments.
Hence we know that the
subject is: Whether brick-and-mortar bank locations will survive this era of online payments.
Now is the tricky part. We need to realize that this
subject itself is a
clause. A handy rule to remember is that when a
clause is the subject, the subject is always
singular. Hence,
is is the correct verb that should be used.
p.s. Our book
EducationAisle Sentence Correction Nirvana has a section on
Clause as the subject. Have attached the corresponding section of the book, for your reference.