At Admin Panel -> Settings -> Switches is a "Print" option. When enabled, the topic tools bar contains a print option which will allow visitors to print out a copy of the topic details.

As of WSN 9.0.0, you can add a printable version link to any page. Just place <a href="{FUNC_CURRENTPRINTABLEURL}">Print This Page</a> anywhere in any template. To link to a printable version of a page other than the current page, just add &format=print to the URL (if there are no parameters in the URL yet, use ? instead of &.