Every so often, one of our lawyers in China will get contacted by an expat asking what we charge to provide them with a U.S. notarization. If they call me in the United States, I sometimes jokingly tell them we will do it for free so long as they come to our United States office to have it done.
And therein lies the problem.
It makes no sense for someone in China needing a United States notarization to fly to the United States to get that. So what are they to do?
Go to the United States Embassy or to one of the U.S. Consulates, both of which will provide U.S. notarization on English language (only) documents that will be used in the United States. All you will need are the documents needing notarization, proof of your identity (your passport), and fifty dollars in cash, RMB equivalent cash, or credit card. If what you are doing also requires a witness, you will need to bring that too.
The Embassy and the Consulates are also the place to go to get Chinese documents authenticated for use in the United States. If you want a Chinese document authenticated by a United States Embassy or Consulate, you must first get those documents authenticated by the Notarization and Authentication Division of Consular Affairs Department of the Chinese Ministry of Foreign Affairs.
For more information on these things, check out the website of the applicable consulate or the embassy.