There are two ways to use this Liquid Level Sensor with WisBlock.
a) the sensor comes with an 4-20mA to analog out module (I think that is from dfRobot).
You can connect this module to the WisBlock RAK13002 IO module, but it will still need an external 12V power supply for the sensor itself
b) ignore the converter module and connect the level sensor directly to our RAK5801 4-20mA interface module. In this case you would not need the external 12V supply