what on earth... vs what, after all,...

[joham]

This sentence is taken from the Cambridge Companion to Modern American Culture:
Du Bois had described the American Negro at the crossroads, pondering the question, “what, after all, am I? Am I an American or am I a Negro? Can I be both?. . . Does my black blood place upon me any more obligation to assert my nationality than German, or Irish, or Italian blood would?”

My question is:
What is the difference between 'What on earth am I?' and 'What, after all, am I?' I think 'What on earth am I?'= 'I don't know who I am'. But the Chinese translation of 'what, after all,...' in question sentences is also that of 'what on earth', which confuses me. Could anyone tell me the difference between the two and explain what 'after all' means in question sentences?

Thank you in advance.

 

[Tdol]

What on earth can be used to express more emotion -frustration, anger etc.

 

[RonBee]

What, after all, am I? = What, in the end, am I?

What on earth am I? = Somebody tell me what I am.

 

[~Mav~]

What on earth can be used to express more emotion -frustration, anger etc.

I've always thought that it is used as a "smoother" phrase instead of "what the hell". Examples:

What on earth (= what the hell/fu**, depending on how intense the situation is :mrgreen: ) do you want from me?

Why on earth are you going to do there? (I'm surprised, I don't have the vaguest clue why you go there.)

How on earth could he do that? (How the hell could he do such a thing?)

Are my sentences/examples correct, and am I right with my interpretations above?

 

[crazYgeeK]

Make a comparison with the sentence "what am I ? ". The answer is surely something on this earth. So they are the same in meaning, but the "what on earth am I ? " expresses more emotions as our Administrator posted.
I think this question is used when you want someone to know that you are surely something even a key element on this earth but he or she didn't know.
I think "what on earth" works as an interrogative pronoun, but the "how on earth" or "why on earth" doesn't and they make no sense to me.
Can I ask "what in this family am I ? " ?
Thank you very much !