英文文法一問：What i should do (?)

"Tell me what I should do" is the right expression. "What should I do?" is regarded as a question so as you know, verbs and nouns are reversed. But in "tell me what I should do", "what I should do" is a noun clause, meaning the same as "something" in "tell me something". It is like relative clause that "what I should do" is actually describing that "something". It works the same whenever you have to add something before a question, like "do you know what she is doing?", noun is placed before verb like normal sentences.

You should answer.

唔該 (ovo)/

"What should I do?" is a question.
"Tell me what I should do. " is an imperative sentence.

2014-03-29 16:41:17 補充：
Both are grammatically correct.