No need to hypothesise, it's been calculated:
https://ourworldindata.org/consumption-based-co2
https://ourworldindata.org/grapher/imported-or-exported-co-e...
China is essentially importing ~1 GT of emissions, and the USA is essentially exporting 0.56 GT of emissions.
The USA would emit about 10% more and China about 10% less if all manufacturing was local; but that would mean the USA per capita emissions would go up to 16.5 tons per capita from 14.9, while the Chinese per capita emissions would go down to about 7.2 from about 8 tons per capita. (Assuming I read the charts correctly).
I aver that none of this matters either, because all of us need to get down to "approximately none" and this kind of thing is just playing a nationalist version of the "no you" game.