Forums module is not GenericContent based module which make the development harder. Generally you need to create a completely new module because there is not similar built in module. Most probably you will be able to use Comments and IComment object with one of the embedded modules. The sections "Recent Questions" and "PopularQuestions" can be IContent items with comments and you can built them in RadTabStrip control with RadMultiPage. So when someone click on a content title you will make redirect to a new page and there require authentication before adding new post. In details mode all content view based controls supports bookmarks. You need to implement a custom ContentView control where the post comment field will be hidden if the user is not authnticated. You can override SetSingleItemContent method.
the Telerik team