In every instance in the films he is called “Kylo Ren” by various people incl Rey (and once called just Ren by Finn)… EXCEPT that one line I see now in TLJ that Hal mentioned where Rey calls him Kylo to Luke. So it really could go either way. The more formal sounding Kylo Ren, or the more familiar sounding Kylo. To me it sounds too familiar when the KoR calls him Kylo. But I’ll record it both ways. Or maybe all three ways (Ren). The KoR would probably just call him Ren now that I really think about it.