This may be one of those jobs where the story is uncovered by finding it in the interviews. Your subject isn't a linear thinker; neither was Dali. Throw out the conventional shooting script; you can't force this type of artist into that mold. rather, use the right interview techniques, as well as the Socratic Method, to tease out the underlying fundamentals a bit at a time, from each piece "encountered", and then a "debriefing" after having looked at the art together.
And maybe while you're obviously trying to make a documentary, maybe all they really wanted was a catalogue video of the pieces: quiet interludes with montage segments built from close-ups and tracking pans across the work, etc. In which case, you go find OTHER people to depose about their reactions to the work, and giving bits of context, etc.
That was a perfect answer! It's for an NGO think tank I am working with and they focus on philosophy, the arts, performing arts, music, etc. I'm part of the organization, with a few different roles. The NGO website is not a finished product; we're only a few months old. But you can get an idea why your answer was perfect.