Grammar checking questions
Most students at least know some grammar, such as major word classes, be able to identify aspectual tense, subjects and objects, singular and plural, etc. Obviously, higher level students tend to be able to answer more difficult questions.
Generally speaking, however, they are not as effective as concept checking questions. Generally they should be done quickly to maintain concentration.
Students of course may know the name of a grammar point but not understand the concept or not be able to use the grammar correctly. They may also be able to use a grammar point, but be unable to name it or explain it. So GCQs cannot therefore be a substitute for practice.
However, the better students will usually be able to answer some basic grammar questions.