So I'm looking for mechanics for skill challenges, competitive challenges etc for a cooking competition. Coming, originality, plating etc.

Any idea on how to make this interesting?

I think this can be a template for a general non-combat competition.

Part of the competition could be treated as a race, and handled as such, using whichever skills would be most appropriate.

Despair could result in a previously unknown, species-specific allergic reaction; or perhaps an unusual combination of ingredients results in poisoning?

There might be an assassination attempt.. somebody framed.. or maybe just an accident that seems incriminating.

Meddling Rival Chefs!

Porg-BBQ!

Definitely a food fight.

My question is what skill do you use for cooking?

I would go with Survival for cooking. Eating a nice meal can be pretty important for your ability to survive out in the wilderness and stuff, so it seems like the best fit. I guess you could go education as well. Survival for figuring out how nourishing a meal would be and education to figure out how tasty and then charm in the last round for presentation. That way you can get three skills into the cooking show and it could turn into more of a team effort than just one persons chance to shine.

Survival..

or Knowledge (Edu, Lore even..?)

Xenology (trying to prepare a dish that would appeal to a judge from an exotic species).

Discipline (a particularly complicated recipe)...

Coordination (...which requires extraordinary dexterity to prepare quickly)...

Education for non-wilderness settings according to skill monkey

Cool also works, for a fine dining modern plate arrangement. Perception could play its part as well

I wrote up some mechanics for skill challenges here . They work like 'PCs have to accumulate X successes in a Y rounds'. Set a duration (e.g. 3 rounds), number (e.g. 15), base difficulty (e.g. 2) and then have the PCs justify what skill they're using each round. If the skill is really tenuous/the contribution is minor (e.g. Athletics to whisk something) up the difficulty. Then total up the net successes from each check. If they're under the limit when time runs out, they fail. If you want to make it more interesting, ban each PC from using the same skill multiple times (so they don't just roll their best skill over and over).

So the encounter could go 'Today's secret ingredient is... Mynock!'.

Wookie Marauder: I want to use Melee to get a prime cut! (Difficulty 2, 3 successes)
Rodian Pilot: I'll try remembering famous recipes with Xenology! (Difficulty 2, 1 success)
Droid Engineer: I'll set the oven to the right temperature with Mechanics! (A bit tenuous so difficulty 4, 2 successes)

At the end of round 1, they have 6 successes. After 3 rounds, will they have barely scraped victory with 15, or created a true masterpiece with 20+?

You could as suggested in the Food thread, I believe, creating an actually skill for cooking/food which would cover all of the subject. Because while I have seen things like Education , Survival , and Xenology listed, along with a couple others, Outer Rim and Core Worlds would have to be added as well because even among just humans of the EU there are multiple cultures with their own ways of cooking and adding spices that will vary from world to world.

It could just be a one shot skill for that campaign, think Cybernetics suggested in Special Modifications