The reason why the webdock portlet is not getting added to the page is because the required theme modules have not been added as can be seen in the error stack:
"Portlet Web Dock Portlet cannot be added as the capabilities [open_ajax_hub , 2.0, dojo , 1.6] are missing. "
WP8 has the concept of theme modules:
http://www-10.lotus.com/ldd/portalwiki.nsf/xpDocViewer.xsp?lookupName=IBM+WebSphere+Portal+8+Product+Documentation#action=openDocument&res_title=Module_capabilities_wp8&content=pdcontent
So if you try to add any portlet to a page that doesn;t have the required theme modules then this kind of error will be displayed
"Portlet Web Dock Portlet cannot be added as the capabilities [open_ajax_hub , 2.0, dojo , 1.6] are missing. "
WP8 has the concept of theme modules:
http://www-10.lotus.com/ldd/portalwiki.nsf/xpDocViewer.xsp?lookupName=IBM+WebSphere+Portal+8+Product+Documentation#action=openDocument&res_title=Module_capabilities_wp8&content=pdcontent
So if you try to add any portlet to a page that doesn;t have the required theme modules then this kind of error will be displayed