When I've installed Windows 10 Pro to Paralles 13 on macOS mojave(10.14.3), taskbar was not displayed on Coherence Mode. On another mac that I use, taskbar is ok, so I checked the configuration file of Paralles:
~/Paralles/windows10.pvm/config.pvs
I found that the value of ShowTaskBarInCoherence is different. I changed that value from
<ShowTaskBarInCoherence>0</ShowTaskBarInCoherence>
to
<ShowTaskBarInCoherence>1</ShowTaskBarInCoherence>
This setting is fine. I can view the taskbar of Windows 10 in coherence mode.