their seem to be two schools when interpreting the role of the drug itself in the psychedelic experience those who think of the drug as a teacher with a lesson plan and those who think of the drug as a catalyst
the former (eg mckenna, strassman) think that psychedelics contain information which is imparted to the user through consumption, the latter (shulgin) think that the psychedelic catalyzes the expression of intrinsic aspects of the human mind. i would ask him if his opinion on this matter has ever changed. has he ever thought of the 'colorless sold' that is mescaline as something impregnated with meaning beyond what the user brings to the experience.
or what drug he was most afraid to taste.
i would ask him a lot of things.