From Tsim sha tsui,where will I leave my luggage if I visit Ngong ping before going to airport?

There is no good place to store the luggage in TST area, unless you place your luggage in certain hotels.
In my opinion, you can take your luggage to the Tung Chung Station. Next to the Tung Chung Station Exit B, you can find a shopping mall, Citygate, where you can store your luggage.
You can store your luggage there and then walk to take the Ngong Ping 360 to Ngong Ping. After that you can take your luggage and take bus line S1 to reach the airport directly.