Nobody. The US cannot possibly conquer China - what a weird question. China has 1.4 billion people and more than enough nuclear weapons to destroy the US. It's entirely possible we can defeat China in a limited naval war by blockading them and blocking or defeating an invasion of Taiwan but that's a very different scenario. And also very dangerous.
Well that was Victoria Nuland's plan, start the Ukraine war to take out Russia and the take on China.
I think crazy in either part of the plan, but here we are supporting Ukraine and pushing NATO into the fight.