If the USCIS Officer does not accept your current 公證, then you may ask someone in China to 叫國內當地派出所出個證明, and mail it to you. Then, you can ask your friend here to translate it into English, and go to the Notary Public (e.g. bank) to notarize your friend's signature. Your friend also needs to write a statement addressing that he/she knows both Chinese and Englsih very well, and the translation is accurate and is in conformity with the original.