1. To determine whether to use whoever or whomever, here is the rule: him + he = whoever him + him = whomever Examples: Give it to whoever/whomever asks for it first. Give it to him. He asks for it first. Therefore, Give it to whoever asks for it first. We will hire whoever/whomever you recommend. We will hire him. You recommend him. him + him = whomever 2.When the entire whoever/whomever clause is the subject of the verb that follows the clause, look inside the clause to determine whether to use whoever or whomever. Examples: Whoever is elected will serve a four-year term. Whoever is elected is the subject of will serve. Whoever is the subject of is. Whomever you elect will serve a four-year term. Whomever you elect is the subject of will serve. Whomever is the object of you elect. from http://www.grammarbook.com/grammar/whoever.asp

when we ask about subject ,we use "whoever" but when we ask about object we use" whomever "

good question.