also say: ?Brad wonders this .?) (d) Brad wonders whether he?ll get the job. (e) Brad wonders whether or not he?ll get the job. (f) Brad wonders whether he?ll get the job or not . Informally, if is often substituted for whether , as in (d) and (f), but not (e). 3. As the object of the preposition. In the sentences below, on is the preposition. ? Whether ( or not ) Alice wants to make the investment? is the noun clause. (You could also say: ?The decision depends on this .?) (g) The decision depends on whether Alice wants to make the investment. (h) The decision depends on whether or not Alice wants to make the investment. (i) The decision depends on whether Alice wants to make the investment or not . If cannot be substituted in these sentences. So, in answer to your question, with the example sentences I asked him whether or not I should go. I asked him whether I should go. both whether and whether or not are fine, since they appear at the beginning of a noun clause used as the object of the verb asked . The entire noun clause?" whether ( or not ) I should go"?could be substituted with this : "I asked him this ."