How's it going? - a general polite greeting,or if more serious about a particular situation eg,'how's the lockdown going ?' How's it coming? - I would not say this,it is incomplete. How is it (where it is a specific activity/project) coming along/on? Example: 'How's the kid's homeschooling coming along?' Hope this helps, Richard

"How's it coming along" or "how's it coming" is referring to an activity, like "how is the activity." How are you if fairly straightforward and I don't think I need to answer that for you.