they always let me do ( what i think i should ) 父母经常让我做(我认为我应该做的事)。what i think i should 做Do的宾语。do 后面要跟个名词从句, 直接排除 when , how,这里that 前面缺失宾语(anything比如),无法指代,你可以说they always let me do anything that i think i should.
what及其后面的部分是一个宾语从句。是动词do 的宾语