studying/studies - most/the most important

Most important WHAT?

Studies/Studying provides the student with knowledge that they can use throughout their life regardless of the career path that they choose.

The first sentence is awkward, but it expresses a superlative--studies are said to be more important than anything else.

The second sentence merely says that studies are important.

The third sentence, like the first, is awkward, but it expresses a superlative.

The fourth sentence, like the second, merely says that studying is important.

No one of those sentences can be said to be correct, in preference to the others. They can all be said to be correct (if rather goofy). If this is a part of an assignment, I suggest to you that whoever prepared it is not a native -speaker of English. The first and third sentences, while not incorrect, are awkward because they do not state what it is that they are most important for. The second and fourth sentences are innocuous--they merely say that studies or studying are important.

Studies, a noun, refers to any number of activities, and may refer to on-going research, completed research, or to the activities of students. Studying, a verb, has an entirely different meaning, and does imply the activity of research, the completion of research or the activities of students. Studying is therefore ambiguous, and is not equivalent to the noun studies.

Once again, this does not resemble the speech of a native-speaker of English.

Thanks, Setanta, for your very detailed reply.

It is not part of an assignment. The sentence was written by a non-native speaker of English.