Staying at the Holiday Inn Shanghai Pudong Kangqiao. Where is the closest Big bus tour stop?

Well, there is no nearby sightseeing bus stop nearby your hotel. You are advised to go to the Bund Area and take it. One of the bus stop is Opposite Peace Hotel.
From your hotel, you can take bus Long Hui Special Line from Xiuyan Road Middle Henghe Road. Then transfer to metro line 2 to East Nanjing Road Station, Exit 6. After arriving, walk northeast around 950 yards to find the destination.