I want to discuss already answered question. Is there any place to discuss it?
Is there any place to discuss already answered question on askubuntu or other stackexchange sites
Ask Ubuntu chat. You need 20 reputation though.
How's Ubuntu Discourse different from other sites?
Ask Ubuntu, the Ubuntu Forums, and project mailing lists are where we do our tech support. We recommend those sites for questions about how to configure and use Ubuntu. This is a place where you can share screenshots, talk about your favorite desktops and tools, and generally hang out with your Ubuntu friends in a friendly, relaxed environment.
Ubuntu forums. I would not visit the ubuntu forums unless you want to re-ask the question and re-discuss it (they probably will not accept a "look I read this on AU what do you think" type of discussion; you have to be more like as a new question with references to askubuntu).
As you might know, we don't really do discussions on the main Ask Ubuntu site, but there are places you can have them:
The Ask Ubuntu Chat is a good place for post related discussion, but you'll need 20 rep to access it. Go edit a few questions!
Ubuntu Discourse a great place to discuss things, questions or otherwise.
and then of course there is the Ubuntu Forums, another great place for discussions.