Hmm. 
I’m not 100% sure I’m right on this, but I don’t think there’s a record of that.
Unfortunately the Pro plan doesn’t include the data explorer plugin, which is the main way to create custom reports, so even if the data does exist you may be a little limited if there’s not an existing one included in the dashboard reports.
Though as a hosted customer you can also contact the support team directly at team@discourse.org (or send @team a message while logged in here on meta). Hopefully they’ll be able to give you a definitive answer. 