いったい
文法の解説は英語です。
用法
いったい is an intensifier used with questions. It usually occurs immediately preceding the question word, but in may appear in other locations before the question word, as seen in Ex 2. "(What, who, where, how, etc.) on earth
例文
そんなにやせてしまって、いったいどうしたの?
You've lost so much weight, what in the world happened?
いったいあなたは何を考えてそんなことをしたんですか
What on earth were you thinking doing such a thing?