What kind of evidence should be required to prove sexual assault occurred?

Well, witnesses, or people that she told of the incident.

Waterboarding the suspect.
Especially for male suspects.

@Dutchess_III But as you know there often aren’t witnesses and people are often ashamed to tell.

This article if you read it all is pretty compelling about Kavanaugh’s testimony being full of holes.

This answer has nothing to do with Kavanaugh or people who wait years to accuse, this is about people who do it right after it happened.
Accusers should have a rape kit and (at a minimum) someone they told because not every rape has a direct witness to the event
EDIT:
Rereading I see you want people who do wait years, my bad.
The second part of it still stands. At that point, after waiting years, witnesses is really all they have unless they documented it in another way.

Very difficult, I would think, to come up with hard evidence (especially when precious time has passed).
Witnesses, like @Dutchess_III mentions, could count as evidence.
The shit thing about this being so hard to prove assault (long) after it happened, is that the attackers also know this (low probability of being caught).
I’ve been breaking my head over this for a long time throughout my life, and I can’t seem to come up with something to better it.
If a victim of assault immediately would go to the police there could be prove of what happened still around.
But I get that there are many reasons why victims don’t/can’t take that step.

So the only thing that my simple mind can come up with is that all mothers and fathers, and other caretakers, and teachers, teach their/our children that it can never, under any circumstance, be justified to touch an other person, no matter how small the touch.
It has to be obvious, very much so, that without someone’s permission we can’t invade that person’s privacy.

It disgusts me to know that some people (knowingly) put other people through hell for their personal (sexual) power trip.

Oh, I know @janbb. I’ve been in those situations. But in this case there WERE witnesses, at least to some of it. I would think testimony from others having seen him in similar situations. And, also, friends she may have told about the incident at the time.

We had an ultra conservative acquaintance call asking if she could drop by after church today. Knowing I was playing with fire I asked what she thought of the situation.
She said, she didn’t believe Ford, but Kavanaugh, on the other hand, was just steady and unflappable.
I guess that’s the blind mentality we’re dealing with here. I don’t understand.

@SergeantQueen She wasn’t raped.

@Dutchess_III and I said it had nothing to do with Kavanaugh, as in, nothing to do with Ford either.

Thank you @rebbel.

Oh God..this acquaintance put herself in a role playing mode and said SHE would have asked “Well, if you were as sexually traumatized as you say you were, how did you go on to get married and have 3 children??!!”
I stared at her and said, “The same way I did.”

Rape is a form of sexual assault although on a higher level.
If you want to talk about a sexual assault that isn’t rape, like groping, attempted rape, etc that’s way harder to prove unless you have witnesses or physical evidence.
He said/she said (with no physical evidence or witnesses) is really really hard to prove because no one wants to put a potentially innocent man/women in jail.

On top of that are legal system is supposed to prove beyond reasonable doubt that the person did it. So if they can’t, the jury is instructed by the judge not to say they are guilty if they have reasonable doubts.

Well, he isn’t on trial for it. Whether he did it or not, yesterday showed he didn’t have the mental soundness and restraint to be a judge on the Supreme court.
Check out the Model Code of Judicial Conduct from the bar association.

The bar wants him looked at more closely too. If he still wins the seat I think hell will break loose.

Witnesses and/or DNA evidence.

And if neither is available, do character references count for anything?

Indefatigable, rather than the dramatic bullshit yelled out by the men hating snowflake victims.

@Dutchess_III Maybe, if the court permits such testimony..

I don’t know @kritper. It would be so easy to argue that “The fact that he did that exact same thing to another women in front of 20 witnesses is NOT proof that he did it to THIS person.”
This week should prove interesting.