Thank you everyone for your reply
I checked a Softbank SIM card, I was able to make phone calls and connect to internet using cellular data. A website I checked confirms the compatibility with Softbank network. however I am not sure about this information.
For other countries it may be the last letter of ASUS_I005D written on the box which could indicate the model of the frequency bands, example France, ASUS_ID005DA
So since my phone's model number ends with "A" then my network version is "A", is this correct?
I checked using CPU-Z as recommended by Lord_messi but it doesn't provide any relevant information.
On the other hand I checked a website about Rog phone 5 compatibility with KDDI/au network, it shows that 2g is not compatible as you can see from the image. However I am not sure if this information is correct or not.