When trading, is the response "I don't see how we can make this work" a final answer?

Short answer: Yes.

Long answer: Yes, but...

I find that this response means that they firmly dislike you, but they would be willing to accept the trade if you had significantly more to offer them.

For example, when I go for a culture/tourism victory, I want to have an Open Border agreement with everyone for additional tourism per turn. For allies, I can offer Open Border for Open Border, or perhaps for a strategic resource or 2 gold per turn.

Usually for the civilizations I've gone to war with recently that hate me, they will say "I'm sorry, there is no way to make this work" no matter what I offer them. However, if I have a commanding amount of resources (eg 4 luxury resources and over 280 gold per turn) they will usually request this just for Open Borders.

Sometimes, you can make it work.

The AI will respond "I don't see how we can make this work", if it believes that a fair deal cannot be made. If the reason for this is that he values his trade offering more than anything you have, then you cannot change it.

However, if you are offering something more valuable than everything the AI owns, like a major city, he may say "I don't see how we can make this work", but then agree to an alternative offer that is unfair to YOU. He will not agree to an offer unfair to him.

Changing the trade offering on either side can still result in a workable trade after the AI has made that assessment.