What could Dinah and Diggle be discussing/arguing about? No idea, but one thing is for sure and that is that Diggle is clearly in his explaining mode. Observe the hands.
Out of all the great things Dinah has done so far in Season 6, it's keeping it real to Diggle. It looks like this episode may have another one of those moments.
Oliver: I have an old friend in town that needs my help and I might not be back at the office for a few hours. Do we have any idea who the shooter was targeting? Rene: We're working on it. Oliver: Good. Be the mayor until I get back. Rene: For real? Oliver: No...it's a figurative speech. Just don't make any laws while I'm out of the office, OK?