A. what time do you usually sleep?

I sleep at 10:30 ​(Punctuation)

B. 1.Nice meet you too, Simsoon. ✔

     2. Who are you?

       => Another way: Your sentence is okay and this is another way of saying it.

             Who's this? 

     3. This is Sejong king.​

          This is King, Se-jeong.

        => Corrected : The sentence is corrected grammatically. 

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