北京条约 is an event for 
China or 
Manchuria (in Vanilla Manchukuo. It will happen to China, unless Manchuria is independent and not a substate of China.
It comes when 
Russia enacts the decision The Peking Convention. The decision in question can happen, when Russia has sphered Manchuria (in Vanilla China or Manchukuo)
The two possibilities are:
- We have no choice, sign their treaty secede the state Outer Manchuria to Russia
- The Czar can go to hell which gives Russia an acquire state Casus Belli by provoking the Russian event China Rejects the Convention! On top of that the relation between China and Russia will decrease by 200 and will decrease Russias diplomatic influence in China by 200.
The AI will almost always take the choice of seceding the state (90% chance to accept). If China decides not to secede the state, one should note that the acquire state casus belli can be used on any Chinese state, and then Russia can use the restore order casus belli afterwards.