ANSWER: Indica gallery.
STEP-BY-STEP EXPLANATION:
The exhibition was held at the Indica Gallery, in the basement of the Indica Bookshop in Mason’s Yard, just off Duke Street in Mayfair, London.
John meets Yoko Ono on the day before her exhibition Unfinished Paintings And Objects was to open, Japanese artist Yoko Ono was introduced to John Lennon for the first time.