According to Osho, 'What is, is what' is Zen’s way of pointing to the formless, unnameable suchness of existence. It avoids loaded words like 'God,' which trigger images and beliefs, and calls you to meet reality directly, beyond concepts. Only lived being, not borrowed language, can express it; the question tests whether one answers from experience (presence) rather than repetition.
It means: drop labels and pictures in your head and just notice reality as it is, from your own direct experience.