I don't know which is the best answer 和I don't know which the best answer is 那个从句的语序正确

问题描述:

I don't know which is the best answer 和I don't know which the best answer is 那个从句的语序正确

第一个正确.
这里宾语从句的原句是疑问词作主语,所以语序不变:
Which is the best answer?
-- I don't know which is the best answer.