The current server version of Confluence does not support adding people to watch a space (from that menu, at least). The Cloud version of Confluence does allow you to do this, but that feature was released only a week ago!
There is an option you could use until then, though, if you really need it.
I wrote a user macro to allow admins to be able to manage watches for other users, including adding/removing space watches. It's here:
Just save it as a user macro under some name (and set to only show to administrators), add it to a page, and then you should be able to use it without any problems
More and more people are building their careers with Atlassian, and we want you to be at the front of this wave! Important Dates Start the Certification Prep Course by 2 April 2019 Take your e...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs