If you've seen him 4 years and are comfortable with his style and now know he obviously "knows" then I would ask him! Start with something "easy" like asking how long you were coloring and where the coloring book and crayons came from? See what he says and then ask him whatever you're curious about (if your alter gave her name or what she may have said, etc.). Just explore "gently" and see where it/he takes you and if it gets too much for you, save some of it for some other time and go back to something "safer" that you were discussing last time that interested you or that you wanted to explore further.