Ele começou a treinar com o Luke. Do script WGA:
HAN
There was nothing we could've done. (hard for him to say)
There was too much Vader in him.
LEIA
That's why I wanted him to train with Luke.
I just never should have sent him away.
That's when I lost him. That's when I lost you both.
Além disso, na novelização, Snoke explicitamente discute com Kylo Ren que ele o esculpiu com base em seu treinamento com Luke.
"It is your teachings that make me strong, Supreme Leader"
Snoke demurred. "It is far more than that. It is where you are from. What you are made of. The dark side--and the light. The finest sculptor cannot fashion a masterpiece from poor materials. He must have something pure, something strong, something unbreakable, with which to work. I have--you"
Mais confirmações do TFA Visual Dictionary:
Having studied Jedi skills as well as arcane dark side lore...
e seu treinamento com Snoke é mencionado também:
Kylo Ren is the most gifted apprentice of Supreme Leader Snoke... (of course, we can also see the same from film dialog)