It depends, you can either say: not much, you? nuthin' well you can really say anything you want. Just be yourself.
"Long time no see" is very similar to saying, "Hello". You might reply, Hey, man, what's up?
you can reply simply You too or with any idiom you feel is right ...
When some says "wassup" you would reply as if someone asked you " what's up."
If someone says sup in chat then the reply is usually nuttin. Sup is short for whats up
You can reply to "How do you do?" by saying "I'm well, thank you. How about you?" This is a polite way to acknowledge the greeting and show interest in the other person.
We should also reply how do you do as a responce.
By saying "Sup". This is a basic friendly greeting where the person is asking What's up or How are you doing? You simply reply back with "Sup"(What's up with you?), or you can say "Nuttin Much"(Nothing much). Do NOT end your reply with "Dog"(friend) back to the person or you will sound like a fool. Person 1 greeting - "Sup Dog" Person 2 reply - "Sup".
Don't reply!
"I am well, and you?"
"Que pasa" means "what's up?" or "what's going on?" You would reply however you would reply to either of those questions.
When you 'reply', the reply is only sent to the person who wrote the mail. When you 'reply to all' the reply is sent to the person who wrote the mail + everyone who received the mail.
Reply what are you doing now or a simple "sup"