你其实已经对了。
但是为什么可以省略呢?为什么是省略的that呢?
(Is there) anything I can do for you?
首先从句部分是I can do for you.I是主语,can do是谓语,for you是状语。从句缺宾语,所以选关系代词,关系代词有which, that, who(whom), whose.这些关系代词中如果先行词是人用who(whom),that,是物的话就用which, that。that既可指人又可指物。但这里必须用that。因为先行词是不定代词。
疑问句
Is there anything i can do for you?
口语化省略掉了is there。
是的,是个省略了that 的定语从句,