From the map, there are 21 fediverse servers in Taiwan but none of them are Lemmy. There are even fewer in China (only 4 based on this map if I select "All" in the option).

AFAIK there aren't any Chinese language content about Lemmy yet.

The center of Fediverse of Asia seems to be Singapore and Tokyo.

Also how can I know which servers are federated\defederated to most of the Lemmy instances?

Exactly the same. Created an account on Lemmy.ml about a month ago but can't login today. So I created another account with the same username on lemm.ee just now and it works fine.