can i complete all the must see attraction of Jiuzhai Valley National Park in one day?

Generally speaking, one day is a little bit tight to tour around the whole scenic area. You may only be able to generally see the must-gos. Two days are the perfect timing! Anyway, Mirror Lake, Five-Flower Lake, Magic Mirror Cliff (Baojing Cliff), Five-Colored Pond (Wucai Pond), Rhinoceros Lake and Spark Lake are must sees. BTW, there are battery cars inside the park to save time.
Have a nice trip!