@JohnLincoln thanks for posting the English data sheet, but it is for a slightly different model (KRTL versus KRTW).
However, both have the same specifications for the output function:
…/2… pin 4: GND if mark detected
…/4… pin 4: UB if mark detected
…/6… pin 4: IO-Link SIO mode, UB if mark detected
…/6… pin 4: IO-Link COM2 mode, see configuration file IODD
I haven't been able to figure out what .../2... etc. means but the second and third options, "UB if mark detected" suggests that that output is active high (UB being the power supply voltage). If so, at the very least a voltage divider will be needed to bring the output level down to 0-5 V.
By the way, the "high side switch" that I posted should work for data input to the module as well. Connect the base of the NPN transistor (no base resistor needed with this circuit) to TX on the Arduino and set the Arduino to 38.5 Kbaud serial.