Sure, the question is just to fix the sentence. But one thing I didn't mention is it underlines a portion of the question, and says please fix this to fix the overall parallelism.
Dr. Crock's claims have been not corroborated by other scientists or published in a prestigious journal but have nonetheless garnered a great deal of attention from the public.
then the question says basically the underlined portion has a parallelism problem, fix it.
Ok. This problem is from Page 60 Manhattan GMAT
Parallelism Problem set.
Rule: Some verb or forms derived from verbs have more than one word: was opening, can lose, to increase. You can often split apart these expressions, so that the first word or words count across all elements.
In our context, we can break the sentence in 2 parts.
So part 1 is: Dr. Crock's claims have not been
corroborated by other scientists or (BEEN)
published in a prestigious journal. (we dont need to use been
in the 2nd half because of the rule mentioned above)
Part 2 is: Dr. Crock's claims have
not been corroborated by other scientists but have
nonetheless garnered a great deal of attention from the public.
The trick is to look out for conjunctions and other parallelism markers, so that you can make the sentence grammatically and structurally equivalent.
Hope this helps.