Truslow
It depends upon what type of SEO job you're applying for and what the test is designed to determine.
If it's more of an entry level job that you're going for, the test is likely designed to see where your strengths and weaknesses are and to learn a bit about how you prioritize those things you know about. If that's the case, then just analyze it from the perspective of the skillset you have and do your best.
If it's a job where doing these complete strategies as part of your job – and you're feeling overwhelmed – then the truth is that you're almost certainly not ready for the job. So it won't matter much what you do, there.
Keep in mind that in Search Engine Optimization (SEO), your job isn't to check things, identify the problems and then call it a day. You do that in order to look at what's there now and see what's pretty good, what's pretty bad – and then figure out and prioritize a strategy to actually fix the bad and turn the pretty good into greatness.
So, this means that as you go through your audit on the test site (as you would look at any site optimized or not) and you see things that are missing – those go first maybe. Things that are pretty good – you can lower the priority on those. Etc.
SEO is as much an art as it is a science. If your idea of SEO is to work from a checklist and see if it's good or bad and then just doing a specific set of things when it's bad – you're not really positioning yourself as a great artist.
I have never looked at a web site – even one where they spends hundreds of thousands of dollars per year on SEO – where I couldn't find a list of things that could be improved or done a little bit differently to improve overall results. And even after executing a six or twelve month strategy that I devised, when it comes time to review and figure out the next steps, there are always more things to be added into the mix to improve what we already started.
The test you're taking is surely designed to determine how well you can do that – be it for an entire strategy, or just to determine which of the many parts of SEO you are good at and which parts you're not.
HINT: There are very few – if any – SEO professionals that are equally proficient in all the areas of SEO. For example, I fully understand the importance of links and how they all work, but the finer points of how to get the links and develop a strategy to build them… no way. So when I have a client and I identify that we need a heavy link building strategy – I'm not going to design that strategy, I'm going to say that it's needed and then defer to the link building experts to develop the specific strategy that fits into our overall plan. If there were more than a dozen or so people in the world who are actually Mr. Miyagi Level Experts in every facet of Search Engine Optimization (SEO), I'd be shocked. I can only name 3 or 4 – well, maybe 7 if I count people who are retired or who have passed away.

Maric
See what are the goals of that client's business. Or, at least, the most important objectives.
Then, make a strategy that can work toward reaching the goal/objectives.
– maybe it's gonna be keyword research to identify new opportunities
– maybe it is on-page optimizing with existing content
– maybe it's content architecture improvements – there's a lot to do in information organization if you are dealing with, say, e-commerce
– maybe it's Call-To-Action (CTA) optimization (shit's ranking but it aint converting)
– maybe there's a lot of shitty pages and it's time to de-index and prune
…all this assuming the basic tech stuff is there.
Finally, here's something people liked when I did these kinds of tests – they appreciated execution input along with strategy, give them a taste of that if you can. Meaning, for example, don't just say "we need to produce these 100 pages to increase traffic," but rather "We need to produce these 100 pages to drive more traffic to our more converting pages, and it will cost us XYZ to produce but the return can go as high as XYZ if we hit just 10% of our traffic acquisition goals." If possible of course 😊
Be creative.
Then use data to explain.
Hope this helps ✌️
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Walsh
'Already optimised' suggests the site is in good shape technically. So now you advise on how to make the content of the site have more value by
a) increasing the amount of useful information on the existing pages,
b) adding new pages with ancillary content about the main topic(s) of the site,
c) adding local pages if the site is hoping to pull business from one city or one country,
d) building Web 2.0 links and social media links to the interesting content and so drive more traffic
e) adding (creating/commissioning) new video content which holds visits for longer durations
f) think/advise on appropriate ways to add interaction to the site (unique and novel tools that let visitors 'play' such as a calculator or colour selector or even to choose the next content from a scrollable selection box (playability increases on page clicks)
g) advise on Pay-Per-Click (PPC) and Social Media Advertising for campaigns related to events and activities of the company or organisation as part of the lead-up to these events.
Get cracking and win! 🙂
Good luck with it too!

Castillo
Look for keywords ranking in position 6 – 15 and find ways to improve those pages. These are low hanging fruit opportunities.
Do content gap analysis and keyword research to find additional topics to write about to generate more traffic. Consider how those keywords play into existing content silos.
Look at pillar content or hubs in silos and identify additional sub topics, keywords or entities that haven't been covered and add them to your content calendar to improve the rankings for those hub pages.
Analyze internal linking for optimization opportunities.
Consider a technical audit (optimized sites over time become less optimized)
Do a backlink analysis on competitors and identify backlinks that are giving competitors and edge and put together a plan to either acquire links from the same domain or domains of equal/similar value.
Do a schema audit and put together a schema strategy to power key pages.
I could keep going, but what I've shared here should keep you busy for a few months, LOL

Joonas
What are their goals as a company? How much they need to grow / increase profitability/ what ever in 2022?
What is their marketing strategy overall?
Then based on goals given you, evaluate what needs to be reached on organic search to meet those goals. How much traffic & conversions are needed.
Then take a look at their current rankings & evaluate content gaps. Where and what needs to be ranked to meet the company goals.
Then figure out what is the plan to increase those rankings.

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