You can simply copy the link of a question or discussion from the browser address bar.
If you want to link to a particular answer, you can click on the date of the answer and it will redirect you to a permalink to that answer.
Tribe also supports short urls. If you provide a separate domain or subdomain to your point of contact in Tribe, we'll be able to add the domain as short url domain. With short url feature enabled, every content page in Tribe will have a short url where users can easily copy and paste.
The facebook sharing should be enabled for all public communities by default. Could you please put a link in comment and explain the missing functionality in more detail.