What planet takes 28 days to go round space?

The planet that takes approximately 28 days to complete an orbit around the Sun is not a planet but the Moon, which takes about 27.3 days to orbit Earth. If you're referring to a planet specifically, the time it takes for planets to orbit the Sun varies; for example, Mercury takes about 88 Earth days. However, no major planet in our solar system has a 28-day orbital period.