First, be sure your resume clearly shows you meet the listed "qualifications." I've seen people not make it through the first application review because a HR person couldn't tie their resume to the qualifications (when I knew they were qualified). Don't count on the first reviewer to understand how your experience with "Y" is equivalent to "X" as outlined in the description.

Then I'd look to the "duties" or maybe for this job its called the "job assessment."

They're looking for the keywords in the job posting, but it's a manual review, so you can use slightly different phrasing as long it's clear to HR.

I would use words and phrases like "wear many hats," "fast-paced environment," "high-stress situations," "tight timelines" to convey these criteria.

I understand I need to incorporate keywords into my resume. Do I use keywords from the job assessment (questionnaire) or do I incorporate keywords from the list of items by which they will rate candidates? The list of items includes "flexibility" and "stress tolerance," and those seem like odd phrases to add to a resume.

Using keywords from the job assessment seems to make the most sense because that's closer to specific skills (financial analysis, contract administration, analyze facts) whereas the list of items they rate you by seem more like soft skills.