Your answers...
1- "Slave Labor" means prison labor, both in China and North Korea (which marks many of its goods as Made in China for sale in the West).
2- China's labor force numbers approx. 760 million. There are approx. 6.8 million people in Chinese labor camps and an unknown but significant number in North Korea.
3- Is slave labor more productive than free labor? Who knows. Certainly, the labor cost of such a workforce is close to zero. And you can't compete with that.
So, according to your figures, slaves account for 0.89% of all workers in China. That does not sound like a serious threat.
3- Is slave labor more productive than free labor? Who knows. Certainly, the labor cost of such a workforce is close to zero. And you can't compete with that.
I would argue that free economies are more productive than less-free economies. That is one reason the Soviet Union no longer exists. And it is a reason why China will have a difficult time surpassing the United States as an economic power. (Assuming, of course, that the United States remains free.)
As for competing with slave labor, that should not be a problem. The labor costs of slavery are not quite zero: slaves have to be housed, fed, and guarded. Otherwise, the slaves will die or escape, and the slave masters will have to find new slaves. Unless the new slaves are employed solely as unskilled labor, they have to be trained just as a free worker must be.
Moreover, labor costs are not the only variable; output and quality are crucial. There are few incentives for a slave to work as hard or as carefully as a free worker. And even if it were possible to force a slave to work hard, he cannot be forced to innovate. That is, a slave will do exactly what he is forced to do; he is not likely to do more of his own accord.