For kxdocker-0.35 and up. Based on gdate theme posted on Stefano's site in Italian, except this is in English. As of this writing kxdocker-0.35 appears to include a broken resources-0.12 file that includes the old incompatible gdate format png which results in a blank icon. The new gdate format displays the day of the week in addition to the day and month.
I did something like this to get to work on my box.
Extract contents into ./plugins
mv ./plugins/gdate ./plugins/gdate-old
ln -s ./plugins/gdate-en ./plugins/gdate