How do you determine if a given Windows Phone running Windows Phone 10 supports USB OTG? I am aware that only a subset of phones support the protocol, but I haven't been able to find a list of which devices this includes or which specific features determine this support.
Most phones support USB OTG and I'm pretty sure every phone released in the last 2-3 years support USB OTG.
The easiest way to determine whether a phone supports it or not is to simply try it out and see for yourself. Buy yourself an OTG connector and plug it into the phone and then test it out to see if it supports it.