What are some questions I can ask someone to find out if they're in a domestic abuse situation?

Specifically, this is my ex, and my kid’s mom. She’s in a relationship that is now six months old and I’m starting to see red flags. She’s become a lot less visible and available than before, and her communication has gone down to almost nothing. From what little I’ve seen of them together, I’ve detected possible signs of codependency and over-attachment. Any time she contacts me or wants to see me, it’s clear that she’s doing it behind her partner's back, and there’s absolutely nothing going on between us to threaten a relationship.

I’m a domestic abuse survivor myself, and one of the things I know is that it’s not easy to be aware or or understand what you’re in when you’re actually in it. So obviously it’s not like I’d just say, hey, are you being abused? So hopefully someone with experience with this knows the right things to say or ask to find out what’s really going on. And my kid’s there with them too. I’m actually taking him on vacation next week (he’s five) and wouldn’t mind finding gentle ways to find out what he sees.

I’m going to get a chance to hang out with her in a couple of days and I’d like to be ready by then. I hope I’m wrong and she’s just being an asshole. Because that I can handle. Thanks all.