They are both grammatically correct as shortened forms for:
What did you say?
Pardon me, I did not hear that. or Pardon me, can you please repeat that.
Only in the most casual settings should you use the shortened form, in any other setting, public, professional, etc. you should use the complete sentence, whichever one you choose.
No, it is not grammatically correct. The correct way to say it is "your older sister."
It is grammatically correct to say: There is nothing wrong with this machine.It is not grammatically correct to say: Will it is be grammatically correct to say ....The correct way to write that or say that would be: Would it be grammatically correct to say....
This question is not clear on exactly what you are asking. What type of sentence are you using the word "what" in? If you are simply asking can one say "What?", then yes, that would be correct but not very mannerly. It is more polite to say "Pardon?" or "Excuse Me?".
'What a drunkard you are' is a grammatically correct English sentence.
No, it is not grammatically correct to say "what a fun." It should be corrected to "What fun!" to make it grammatically accurate.
No. Him and me is correct.
This sentence is grammatically correct.
It is not, but it is widely used because it conveys the general idea of the question as well as its grammatically correct version.No you should say "Where are you" the at at the end is not needed.
No, it is not grammatically correct to say "keep stick to." The correct phrase would be "keep sticking to" or "stick to."
It is grammatically correct to say , "I am in school today." This is because you are in the building, not at the building.
no
yes