Yes, you can sip miso soup, and it's actually the most common way to enjoy it in Japan.
Rather than using a spoon, many Japanese people traditionally bring the bowl to their lips and sip the broth directly. Chopsticks are used to guide the solid ingredients, such as tofu and seaweed, into the mouth along with the soup. This method is considered perfectly acceptable and even preferred by many. While a spoon might be offered in some restaurants outside of Japan, it's generally not necessary or the customary way to eat miso soup.
