I will voice a probably unpopular response.
Note:
This "use case" is written if the OP has to handle someone suffering
from traumatic experiences that can be considered out the norm and
even extreme.
My only credentials is that I have spent a lot of time in psychiatric
care and in hospitals.
It is quite helpful to have been there and done that.
Both specifically and in a larger sense.
It is hard to understand the mindset and the internals
of having to deal with something highly traumatic unless
you have experienced it yourself.
You can learn about it from reading a book sure but it is
at an abstract. It doesn't fill the colors, the anguish,
the sights you cant get rid of.
Exposure and repetition can also help.
If you are a psychologist who have worked with people in deep despair
over time and multiple cases you can start to put more puzzle pieces
together.
If you ask if a person "wants to talk about it" and the person says no.
No means no. Try to find some activity or topic entirely unrelated, or
just give the person space.
If someone does want to talk about it.
Sit down, shut up, clear your brain, and listen closely.
Be prepared for what might be a horrible story.
Be prepared for details you would prefer not to hear.
Be prepared for crying, angry outbursts.
Platitudes can help and can be destructive.
Depending on the person.
Sometimes it can help if the person is responsive.
Sometimes it can spike anger.
If the person responds negatively just stop with the platitudes full stop..
Then listen closely, imagine where the person is mentally, mostly keep quiet
but see if you can say something relevant to where the person is.
Overall it takes time.
Not just a conversation.
Many conversations,
Always wait until the person seems to indicate further interaction, .
Dont nag about it. That is unwise.