The WC section tests your writing ability more than your knowledge. But having the knowledge certainly helps you frame out and write a solid response faster than having to ponder how much BS is necessary to satisfy the requirements, what order to put the BS in, etc.
Always remember that unless your score is borderline, a computer will be the only grader. The computer is programmed to look for proper paragraph structure (topic sentences, supporting sentences), transition words between paragraphs, key terms, definitions, examples, and proper spelling, grammar, and punctuation.
Key terms, definitions, and examples are the places where your knowledge comes into play, but again, a computer is reading this, not a human. So you can get credit for writing something kinda useless if you phrase it in the right way.
For example, say you're writing about depreciation methods. This could be the start of one of your paragraphs:
“Straight-line is one acceptable depreciation method. For example, a boat is an asset that can be depreciated on a straight-line basis.”
That's a fairly ridiculous attempt to explain what straight-line depreciation is, but you'd get some credit for it because you included all the bold terms.
Also remember, if you have no idea what to write, a lot of key terms will be included in the writing prompt itself. Take those, add some high-level color and some creative rephrasing, and you'll be okay.