Depending on your Notification Preferences, when someone responds to a discussion you created, you should get a notification (as you will hopefully see by me posting here). You can also access a list of discussions you have commented on, as well as bookmark certain discussions using the Star icon in the thread's title strip. Again, in your Notification Preferences you can determine which things will give you a notification.

PTS is a separate download, and is primarily used for testing new content before it is released on the Live servers. Currently on PTS at the moment is Orsinium, so there's nothing new to test right now, but after the New Year we will hopefully see the new Thieves Guild content becoming available on PTS. The characters available on PTS are periodically wiped, and when a wipe occurs, ZOS copy characters from one or other of the Live servers. For example, you could have a copy of the NA character database there for a few weeks, then they will be wiped and the EU character database will be copied instead. The copied database includes all friends, guilds, and bank/inventory items. There are also template characters available all the time which can be used, for example, to test out a VR16 character with the content if you are on the rotation where your copied characters are not available (due to the copy being from the other server). The PTS server is entirely separate from the EU and NA servers, so nothing you do on the PTS with your copied character will transfer back to the Live server that the character originally came from.