When communicating in Chinese you may often make mistakes using Chinese grammar like:

False:

    A: 昨天你做什么了？

    Zuótiān nǐ zuò shénme le

    B: 昨天我做看书了。

    Zuótiān wǒ zuò kànshū le.

True:

A: 昨天你做什么了？

Zuótiān nǐ zuò shénme le?

B: 昨天我看书了。

Zuótiān wǒ kànshū le.
“做什么”是动宾词组，用来咨询进行的活动。在含有“做什么”的疑问句里，疑点应当是“做什么”，答案“看书”便是疑问所在。如果疑点仅仅是“什么”，答案自然写成了“做看书”，这是错的。

做什么 is a verb-object phrase which inquires about an activity. In an interrogative sentence containing 做什么, the question lies in 做什么 as a whole, to which the answer is 做看书. If the question is considered to lie 什么 alone, the answer naturally turns to be 做看书, which is definitely ungrammatical.