In the most recent versions (0.44.1) for Mac OS X and Windows, the Whiteboard menu is no longer apparent.
I have tried installing from source but at the configure stage
sudo ./configure --enable-inkboard
I can get no further than
configure: error: libpng >= 1.2 is needed to compile inkscape
I tried but failed to install the latest stable version of libpng.
In the meantime, I have a filed a bug report (which may translate to a feature request).