Are you attempting to "bait" or "troll" me?! Are you sincerely saying that you don't already know and couldn't easily recognize an "extraordinary claim," and don't already have a good idea of what "extraordinary evidence" you would require in the face of such a claim?!
ANSWER: The same kind of qualities displayed by the accompanying claim.
As my tag-line states: If the claim is extraordinary (= displays the earmarks of being extraordinary, as opposed to being banal, obvious, and/or quotidian), then the accompanying evidence should be of the same caliber.
Example:
At a coffee-shop in Berkeley, you bump into a long-time acquaintance, whom you know to be of sound judgement and good repute, who says, "While recently walking through Union Square, in downtown San Francisco, I accidentally stepped into what appeared to be human fecal matter."
That is NOT an "extraordinary" claim, is it? Which is why you probably wouldn't evince extreme doubt and dismay, say that it was astounding. You wouldn't immediately express great skepticism, and demand photographic evidence, a DNA test of your friend (after all: He might be an imposter!), the sworn testimony of three reputable eye-witnesses, would you?
But now suppose that you discovered, at a flea market / swap meet, a clay tablet, purporting to date back to approx. 300 B.C. (it mentions various kings and such from that era, and identifies them as still living), inscribed with a story, in Attic Greek, of how the author undertook a journey to the Moon - say, on the back of a great eagle. In his narrative, the author claims to have actually met the King of the Moon, etc., and describes in detail the lunar flora and fauna, the workings of the lunar society, etc.
I think that you now realize that you already knew what is meant by "extraordinary claims." And that you likewise now realize that you already knew what kind of supporting evidence you would demand before accepting the veracity of the clay tablet.
Regards,
Nope; for what I 'know' has no bearing on what you know.
What works for me, obviously doesn't for you - thus the question.