It goes wherever you put Moderating /Chairing sessions.
Well I don't include that. The question here is that I have to actually give a presentation, provide written comments etc. Was just curious. It's no big deal. May include it under refereeing etc.
If you don't put Moderating/Chairing on your CV, then I would put this on there either. I don't put either on there. But, I do agree it is professional service which could go with reviewing for journals as well. Maybe under professional service to conferences which would include chairing/moderating, program committees, program chair, society officer, keynote speaker, etc.