1---你好----Hello , How do you do?
This is the most common for of greeting in China. It can be used at any time of day when meeting people for the first time or for people you already know. The response to this greeting form is also "你好“。
2---你好吗---how are you?
This is also a form of greeting. often used after you have not seen someone for some time, and the response is usually " 我很好“ or other similar formulas.
3---你呢？ ---and (how are )you?
4---也很好。 ---( I am ) fine ( literally, very good), too.
This is an elliptical sentence, with the subject "我“ omitted. In spoken Chinese, when the context is explicit and there is no ambiguity, the subject is often omitted. One may also say " 很好“ to answer the question "你好吗？“
5---How are you doing?
---doing good. or doing pretty good. or doing well.
The most formal is " doing well.". but the spoken language generally said " I am good."
6---What is up means " What is happening?"
What is up ---not much. or nothing, except I hate my boss. or I am relaxing with my granddaughter. (example or real) . or I am studying. OR specific news. My teacher is a pervert.
Contractions How is = How's. I have been = I've been. use of contraction is idiomatic.
We sometimes prefer contraction, and sometimes don't .
7---How do you say the word" greeting" in China.
Hello. good morning. Nice to see you. I am please to meet you.
When you enter the house you should greet your family.
You would say, Hello. or Good morning, afternoon or evening depending ont the time of day. In England and Australia they say Good Day.
Hey how was your day? How's your day going? How's your day been? How is your day?
You could use any of the greeting you suggested.
8---How's it going---I am working on this stupid report. I am studying my English.
Thank you for some useful advice.
In England we do not usually say "Good day", though people will say 'Good morning' in a formal situation, or when greeting colleagues on arrival at work. 'Good afternoon' and 'Good evening' are rarely used, although the presenter on TV or radio may start a programme with this courtesy greeting.
The initial greeting might be followed up with 'How are you ?', to which the reply could be 'I'm fine', 'I'm all right', 'Not bad', 'Not too bad', etc. Even if you feel bad, you would not normally get into that in reply to a courtesy enquiry. If you are speaking with friends or family then it is different.