SEO

I imagine the would expect you to know at the very least what the search volume is for the terms and what competition there is for them.

You can research word and phrase popularity through the Google Keyword Tool.
SEO really depends on knowing which relevant phrases are most popular (and which are middling popular), so you can use a wide range of them and not be penalized in searches for 'keyword stuffing' (using the same word/phrase over and over). It can also help you to aim an article towards a niche area of a topic.
I'd imagine most employers would expect people to know how to use the keyword tool (easy to learn), or a similar site, or how to optimize in a different way.
But, ultimately if you can consistently get articles on the first page of search results, that's the aim of SEO, however it's done.

A friend who lists titles for a book distributor says she just wants keywords, not popular keywords. Anything that can take a shopper directly to your book can help.