As mentioned by Wishfull, the "where the heck" sense may be expressed by いったい but note that いったい can be used without lowering the speech level as inserting "the heck" would.
In this contextless sentence, however, いったい does not seem to have much effect on the overall meaning. どこにあるでしょうか is a polite enquiry because of a conjugation of です and the desire of the speaker to know the answer is weak, say, in comparison with a sentence with んで such as あるんでしょうか. I can imagine a quizshow host urging a respondent to tell in which country Machu Picchu is located. He would say, "マチュピチュは、どこにあるでしょうか" because, as the host, he already knows the answer (Why, it's in Canada!). He may open the sentence with いったい, seeing the bewildered expression on the respondent.