1) People outside the US don't celebrate Thanksgiving, at least not on the fourth Thursday in November. Some countries have their own special days for giving thanks, but the November one is a US holiday. Likewise, people who immigrated to the US recently might not be aware of it and not celebrate it for that reason.
2) Jehovah's Witnesses, for a variety of reasons, don't celebrate Thanksgiving.
3) Some Native Americans don't. It is a holiday that celebrates the Pilgrims surviving their first year in the Americas, and it basically all went downhill for Native Americans from there. Plus the Thanksgiving story that is told in schools is not very accurate. Many Native Americans have a Day of Mourning on Thanksgiving, or celebrate just family and togetherness.
4) A lot of people just don't like the fuss. They are not interested in the historical or religious roots of the holiday, don't watch football, and don't like cooking an unnecessarily fancy meal.
Most of the countries in the world do not celebrate a holiday called Thanksgiving.
Those that do celebrate or observe Thanksgiving are: Canada, United States, Libya, The Netherlands and Norfolk Island.
It is unusual to find people in the U.S. or Canada who do not celebrate Thanksgiving.
It is a national holiday in America. Canada also has a Thanksgiving Day but it is not the same day as the American holiday.
Canada celebrates Thanksgiving in October on the second Monday.
Canada and the United StatesCanada celebrates Thanksgiving on the third Monday in October and the United States celebrates Thanksgiving on the fourth Thursday in November.
Thanksgiving
China
Do you mean "when"? If so, Canadians celebrate Thanksgiving during early October.
Thanksgiving has no religious significance and no one religion.
Thanksgiving Day traditionally celebrates the arrival of the first pilgrims to America.
There is no such thing. Only the USA celebrates thanksgiving as a national event.
6 at the most
I'll answer when you correct your grammar.
Canada
Sometime in December.