>someone asks you a question, and you don't quite understand what they're trying to convey
"How do you mean?" vs. "What do you mean?"
Which one is correct?
Sorry, but not all of us grew up on formula food, which means that we are more articulate than those who did such as yourself.
Both are correct, I suppose how do you mean implies a certain ambiguity in interpretation, whereas what do you mean is more for total puzzlement. But those are only waverings on a line.