The idiom how’s it going is another way to say how are you, how are things progressing, or what’s up. The it can refer to life in general, a project, or your day.
It should be noted that this idiom is said in many countries with the answer expected to be fine or good. This is not usually what a person says when he or she truly wants details of your life or day. Often this is said as a continuation of the greeting (e.g., Hi, how’s it going?), and the return answer should also be a continuation (e.g., Good, see you later.)
If the speaker wants further details, he or she will ask again or make it understood by intonation or facial expressions.
In written communication, the idiom can appear as part of a greeting in a letter, but again almost as a rhetorical question that is not expected to be answered.
I see a lot of people when I’m working the lunch during the week. Even if people I’ve seen before aren’t sitting in my section, I always swing by and say, “Oh hey, how’s it going?” just to let them know that I remember they were here before and let them know they’re in good hands. [Cosmopolitan]
Every morning, as we walk through middle campus, we inevitably pass several people we know and engage in a dialogue that fits a construct resembling this: “Hey, how’s it going?” “Good, how about you?” “Good.” After this, we move on. The phrase how’s it going, which has become nothing more than a superficial conversational placeholder for genuine interest, demands a lot more than the usual mechanical and lifeless response it receives. [The Heights]