The option to view if a user is currently log in to QuickBooks Online isn't available for now. Although, you can trace his activities using the Audit log features. Here's how:
Click the Gear icon.
Select Audit Log.
Click the Filter icon and select the user in the User drop-down.
QuickBooks is continuously improving to enhance our customers’ experience while using it. I'll send this feedback on your behalf for consideration in future product updates. I want you to be the first to hear about the latest QuickBooks innovations, so I’m adding an article to view the details: Firm of the Future.
Reach out to me if you have any other concerns or questions. I’m more than happy to assist further.