How to get a visa in a country you are not actually from

I am Canadian, and I applied for a X2 type for China which only allows me to stay there for 150 days. I am leaving to Korea to apply there, how complicated is that? Or should I apply for one in Japan or Hong Kong?
In the "basic documents" it says

3) Proof of legal status (applicable for those not applying in their country of citizenship)
If you are applying in a country that is not the country of your citizenship, you must provide the original and photocopy of your valid certificates of residence, employment or student status, or other valid certificates of legal stay provided by the relevant authorities of the country where the center is located.

I have no idea how to validate my stay??