I'm a non-native speaker. When I was at school, we were taught that "on earth" is used for emphasis in questions such as:
What on earth are you talking about?
However, from my experience (English movies, TV, online discussions, etc.), I seldom see people actually use the phrase "on earth".
From what I see, the most commonly used phrases that express basically the same meaning are "What the fuck..." and "What the hell...".
I don't like cursing or obscenity (call me old-fashioned), so here are my questions:
Is "on earth" still commonly used in real life?
Is there any alternative that is not cursing or obscene?