Enabling the KlikAanKlikUit (Kaku) ABST-604 dusk sensor in Domoticz is easy. That is, once you've figured it out. It took me a little while to determine how to properly process the signals from the sensor.
My setup is a Raspberry Pi 3B+ with an Rfxcom RFXtrx433E transceiver. I assume that you have Domoticz installed, and the Rfxcom configured under hardware.
To allow the signals to be processed by the transceiver, be sure to enable the AC protocol. You can do this by navigating from the Dasbhoard to 'Hardware' and then selecting 'Set mode' in the Rfxcom entry.
In 'Set mode', select the AC option.
Now Domoticz can 'learn' the signal sent by the dusk sensor. In order to do so, navigate to the Switches tab and click the 'Learn Light/Switch' button. After clicking it, you only have a few seconds to let the dusk sensor emit a signal. Toggle the 'Learn' button on the sensor. Domoticz should immediately show a popup which allows you to add the dusk sensor to your switches.
Note that, to do a proper setup, you want to trigger this process under circumstances you would consider 'dusk'. Or, alternatively, the conditions under which you would want your lights to switch on.