Hello,
I don't see how you would be able to do this with a DP -> USB-C cable. As far as I know this cable works the other way: from USB-C DisplayPort Alternate Mode to DisplayPort.
You can connect the
Dell p2419hc with a DP-DP cable to the docking station.
When using 3 displays connected to the Dell D6000, the HDMI output of the docking station will rely on DisplayPort Alternate Mode technology whereas the 2 DisplayPort will rely on DisplayLink technology. Because the 3rd display relies on Alternate Mode, 3 display configurations require the dock to be connected with the USB-C plug.
Kind regards,
Alban