Sellers are required to disclose obvious defects to a house. Do they always? No. So be sure to do your due diligence. If you have suspicions that a certain neighborhood might have chinese drywall, ask your realtor to do a search for that neighborhood and review the available notes for other similar properties. Many properties with Chinese drywall have been remediated, this is often times disclosed to buyers or agents on a listing. This can be very useful in gaining extra insight into an area.
You can also ask to have the drywall tested or inspected during your inspection. There are clear telltale signs.
There is not a specific question about Chinese drywall on the sellers disclosure but IF a seller knows they have it, they should disclose it. Your best protection as a buyer is to get an inspection by a real estate inspector that does an inspection specifically for Chinese drywall. The website that Veronica posted is a good souce of information and has several inspectors listed.