Odysseus, if he existed, and I would ask him to recount his real journeys.
Sappho, the best poet of her time, to look over her shoulder as she writes.
Aliénor d'Aquitaine, to hear the story of those incredible years.
Dante Alighieri, to ask him a reading of the Vita Nova.
Lippo Lippi and Botticelli, just to stare at them while they work.
Giordano Bruno, to ask him explanations about that Shadows of the Ideas I don't twig.
Benedictus de Spinoza, to discuss with him about his own theses and buddhism.
Antonio Vivaldi, to hear the première of the Gloria in Re Minore.
William Blake, to see him draw those drawings, more than for his poems.
Bertrand Russell. I'd ask him how he abandoned mathemathics and philosophy to write SF. I'll lend him a book or two of contemporary authors, and we'd chat.