How to Show Date on Clocks
To show the current date on World Clock select a date formatter on the "Time and date display options" node in
Preferences.
By default, the date in World Clock is turned off. In the example screenshot below, we have a couple of clocks in taskbar, London and local time. Both do not show date.

World Clock without date by default
To show the current date on the local clock, open Preferences, and navigate to the
Time and date display options node for it. Each clock has its own Time and date display options. Make sure to open the correct one for the local clock.

Time and date display options page in Preferences
As you can see from the screenshot above, the
Date field shows None, which means
do not display date. Change the Date field from
None to the format you want.

World Clock date formats
Each line in the Date dropdown represents a date output in a particular format. For example, if you select
d.MM.yy then the date will show up as on the screenshot below.

World Clock date format example
And here is how the resulting local clock in taskbar will look like:

World Clock with date in taskbar
Now the date shows on the local clock, but the London clock is still without date. This can be changed, too, on the Time and date display options page for London clock.
World Clock FAQ