what clause來自一個主係表結構的句子(主語+係詞+表語):
這個句子可以是:
(1)the real bliss in this world to me is my son.
也可以是:
(2) my son is the real bliss in this world to me.
所以用what來替代了my son之後然後提前到句首來lead this clause,就可以是:
what the real bliss in this world to me is.
or:
what is the real bliss in this world to me.
to me 的位置我覺得可以靈活,所以你上麵說的三個用法我覺得句法上都對。具體哪個更好一些,我想跟想強調的方麵不一樣有關,和個人說話習慣有關,得問問native speaker了。