例えばheとhisとhimの違いに近いです。
疑問文を作るときは聞きたいものによって変えます。
誰が(人)
○Who put this on the table?/He did.
×Whoes put this on the table?
×Whom put this on the table?
誰の(物)
○Whose pen is this?/It's his pen.
×Who pen is this?
×Whom pen is this?
誰を(これは少し例外で最近は疑問文のWhomをwhoとして使われることが増えてきたのでWho, Whomはどちらでもいいです。)
○Whom do you love?/I love him.
○Who do you love?/I love him.
×Whose do you love?
