Spinachis a vegetable with large dark green leaves that you chop up and boil in waterbefore eating.

請問這個句子的 eating 后面是否漏掉了賓語 it?

即應該說成：

Spinach is a vegetable with large dark green leaves that you chop up and boil in water before?eating .

你的句子 eating 后面加不加賓語it 都可以：

Spinach is a vegetable with large dark green leavesthat you chop up and boil in waterbefore eating . 菠菜是一種蔬菜，葉子非常大，呈深綠色，吃之前要把它切碎，放在水里煮熟。

有時英語的關系代詞可以同時在兩個結構中用作賓語，譬如你的句子，關系代詞that既用作動詞 chop up 和 boil 的賓語，同時也用作動名詞 eating 的賓語，但動名詞后面帶上賓格代詞也可以（即這個it 可以省略可也可保留）。這種使用方法多見于定語從句連用 after /before / without 等介詞后面接動名詞的場所。又如：

It has a thick stem that you boil in water before eating . 它的莖非常粗，吃之前要把它煮熟。

Pills are small solid round masses of medicine thatyou swallow without chewing . 藥片是一種形狀非常小的圓形固體藥物，不需要咀嚼就能吞下。