So I can change your sentence as "Where on earth are you find it?" "How on earth do you achieve it" Am I correct?"What on earth are you talking about?" is acceptable in all circumstances, even formal ones.
Heck is acceptable in most informal circumstances.
Hell is quite strong, suggesting anger.
Fuck is the strongest, and is very offensive in all circumstances.
Actually by Elmer Fudd (from Bugs Bunny) who was also caught saying, "What in tarnation" as I recall (though I doubt that I could document that).If you mean it's used by people who use out of date terms, no, sorry, that isn't true.
I don't think I've ever heard dagnabbit in my life. Sounds like something from the Hobbit!