1) Justin Bierber held/had a concert in Malaysia last month.
2) How many concert will he perform in next year?
3) How many concert will he hold next year?
4) Who's artist concert was it?
2 and 3. How many concerts will he do next year?
4. Who's should be Whose, but it's not very natural. Which artist performed at the Civic Center last night? Who did a concert here last night? Which artist did you see in concert?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.