What is the highest and lowest temperature in the exosphere? or just the highest temperature.

The temperature within the exosphere varies, depending on whether you are looking at the "day" side of the Earth, or the "night" side of the Earth. Because the atmospheric molecules are so disperse at this altitude, their energy is related to the amount of solar radiation that is received. During the day, the temperatures can reach thousands of degrees Celsius. During the night, the temperatures can reach close to absolute zero.