how can i reach Dongguan, guangdong, china from zhangjiagang, suzhou, jiangsu, china by train or air ?
You can fly from Wuxi Shuofang Airport to Guangzhou Baiyun Airport and then take a bus at Baiyun Airport to go to Dongguan. Shenzhen Airline and South China Airline operate flights between Wuxi and Guangzhou. Flight time is a little over two hours. Airfare should be ¥700 or so, one-way. Wuxi Shuofang Airport is about one hour's bus ride from Zhangjiagang. There should be direct buses between Zhangjiagang and Wuxi Shuofang Airport. Bus fare is approximately ¥50. If you go by taxi, it costs about ¥250.
There are shuttle bus between Guangzhou Baiyun Airport and various destinations in Dongguan. Bus travel time is close to two hours.
Shanghai Hongqiao Airport is about two hours from Zhangjiagang. Bus fare is ¥90 or so.
You can also travel by train from Wuxi (or Changzhou, Suzhou) to Guangzhou. K527 departs from Suzhou Railway Station in the evening and arrives in Guangzhou 25 hours later. You'll need a sleeping berth for this long train trip. A hard sleeping berth costs ¥350 or so whereas a soft berth goes for ¥600 or so. Train ride distance is close to 2,000 km. From Guangzhou and Dongguan it is a bus ride of aobut one hour.