The expected reply to "How do you do?" is "How do you do?" It is only because the greeting has fallen out of favor that you now find people who have rarely encountered it treating it as if it is an actual question needing an indicative reply (as "How are you?" and "What's up?" do).As a greeting, "how do you do?" is very formal, and possibly a bit antiquated. "How are you?" would sound more natural. Your reply would depend on the context, however some usual replies to this are: "I'm fine, how are you?" or "I'm doing well, you?"
"How's it going?" is a more informal greeting. Again, your reply would depend on context, but the usual replies to this are: "It's going well/fine, thanks."
Hello thales1982,please, Is it right to say how do you do or how's the going? how should one reply to that?