You answered B...

Go up to them both and say: Hi, this looks like an important conversation. Can I suggest you continue it in my office – I’m not using it at the moment. And leave it at that.

This looks good as far as it goes – it doesn’t judge either of them and may save much face for them both. We wonder whether people watching from a distance might think that Jo and Hugh have been ‘told off’. We also think that not saying anything to Jo about her management style may allow her to think it’s OK to give loud negative feedback in public and might leave Hugh thinking that he is working in an organisation that tolerates public humiliation.

Our suggestion is C

Nothing at the time but later that day find Jo and say: Jo, I know you’ve had enough of Hugh. However, I was alarmed to see you having it out with him in front of the whole room because being criticised in public probably made things much worse for Hugh - it might also make people worry about whether you would do the same to them if they crossed you. I am keen for you to apologise to Hugh, in some way.