Isolated DC/DC Primary ON/OFF
If you're going to be using the PMBUS version/feature of this supply, you should be able to control the power supply enable state with a PMBUS I2C transaction. This will require some sort of PMBUS master device powered by the 48V input supply. This could be as simple as a low-pincount micro-controller with an I2C interface. You can even bit-bang the thing with two GPIO pins, but I digress...

IF you want to enable the supply using a simple on/off Remote Control signal, you will need some sort of logic circuit on the input side. It wouldn't make sense to have control circuits on the output (isolated) side, because when the supply is off, the circuits are unpowered.

This particular module has a pin called RC (Remote Control). After, reading the data sheet several times to makes sense of the "P" and "N" suffix, it looks like they want you to either ground the RC pin or leave it open to control the output state. You could use a simple BSS138 N-channel MOSFET with the gate tied to your 3.3/5V logic circuit, source tied to GND (-Vin), and drain tied to the RC pin. Just make sure that your control circuit GND is connected to -Vin, which it already should be.

In my experience, we like to set things up so that the lack of drive to the power supply remote input (for example, the control cable fell out) will disable the output. If the MOSFET described above were OFF (logic low at the gate) then you want the supply to be off (I'm guessing). Either way works but one way is slightly safer than the other. I cannot definitively determine which suffix (N or P)would do that from the data sheet. The data sheet is written poorly to describe the feature IMO. Your best bet is to call the Murata tech support and ask this question: "If I use the P suffix module and I ground the RC pin, will the output be enabled or disabled?". 

Good Luck!