Hi, is a shuttle bus from Kowloon to Shenzhen Airport?

Yes, there are.
You can take shuttle bus near Nathon Hotel (B1 Exit of Jordan MTR Station), whose address is No. 11, Pak Hoi Street.
The bus starts from 07:00 to 19:30 every day and the interval is around 30 minutes.

Or you can also take bus at the first floor of Elements (Exit C of Kowloon MTR Station). The bus starts from 6:15—19:45.
Hope it is helpful.