to ask what to say to someone ...

[helloworld2012]

who tells you they just separated from their DH? Not a close friend, an acquaintance, and I didn't know if it was a mutual decision or a shock...She really seemed to want to talk about it but I didn't dare ask questions.

This was the start of the conversation...
me : So, how are you? It's been a while!
her : Yeah, lots of things have been happening. Me and DH separated. I'm single!
me : Ohhhh...

How are you feeling about that?

Or something that isn't saying "oh no/oh brilliant" without knowing how they're feeling about it.

""that must be difficult for you (and the children?) how are you coping?"

Oh I'm sorry to hear that... And they'll often reply that they're glad to be finally rid of them. Then carry on chatting.

Thank you, these are all good ideas. Why can I never think of a good response at the time!

'Oh wow, how are you doing?'