sentence stress

[Dreams come true]

Hello,
I'm a bit confused about the sentence stress rules. I found an information that demonstratives (this/that/ those) are stressed. However, they haven't been stressed here:
That’s great!

What are the cases when demonstratives are stressed?

Also I'm confused about adverbs which I've learnt should be stresses too. Why is it not the case with 'already' in the sentence below?
I’ve already told them you’re going, Ben!

Thank you in advance for your kind answers!

[Dreams come true]

I'd like to ask as well if contractions can be stressed like in the question:
What's the problem?

I know that question words are normally stressed but I'm not sure what's the case here.
THANK YOU!