Thanks for all your help/advice.  We are going to email and offer to sign a message. 

That message I quoted was their last one, after a video meeting with ID, sending them images of prior deposits, etc. etc. etc.

I am aware of basic crypto safety and am fine.  I told my friend not to leave all that on an exchange but he's too lazy (as usual) and now he's paying for it.

Thanks for your response.  I am thinking Bittrex simply doesn't want to release the funds so they ask for the impossible.  Here's the exact quote:

“Is there a screen in your wallet program that shows your wallet address associated with your name or email address or just a list of your wallet addresses?”

Strange story here.  Have a friend who put money into crypto in 2017, and was trading on Bittrex. 

He neglected the account until last month and Bittrex doesn't want to let him in at all.  He's asked them to remove 2FA so he may access his funds. He's sent them screen shots of every transaction he's made with them, appeared on a video call with them showing his driver's license, etc.

Now they are making this odd request.  They want to see his address in a wallet with his name or email on it. I'm not aware of what wallet would even do this.  Crypto.com DEFI wallet displays the user's name, but after inputting the seed phrase it shows no history.