What can I do to apply Chinese citizenship for my son?

Khaled, your son automatically gains Chinese citizenship because his mother is a Chinese. you need to apply for a China Travel Document for your son if you plan to take him back to China. The application should be submitted to the Chinese embassy in Iraq. The materials include:
1. a filled application form for China Travel Document. You can sign the form on behalf of our son.
2. 4 passport photos taken in recent six months.
3. the birth certificate (both original and copy versions). You can get it authenticated by Chinese embassy because authenticated birth certificate is required when you regisiter his Hukou after you come back to China.
4. both you and your wife's passport and copies of both your passports' information page, visa pages.
5. marriage certifcate (both original and copy versions).
6. valid resident permit in Iraq (original and copy versions).

When you take your son back to China, you may go to the local PSB where your wife's Hukou is registered to apply your son his own Hukou. It should be together with his mother. Then you may apply him a Chinese passport.