Yes, you can eat radish greens. They are spicy and good in a salad. You can also cook the greens from the kohlrabi, just as you would turnip greens.
You can make a puree with parsnip, kohlrabi, potato and leek or garlic. Delicious. Just skin, steam until tender, blend, add butter and salt. Better than mashed potatoes from my point of view.