1今天他想在 ( 到 is better) 书店买两本书 is ok
and
2 他想今天在( 到) 书店买两本书 is also ok, but compare it to 他今天想到书店买两本书,the latter is smoother.
谁知道这个问题的回答清告诉我谢谢大家..... By the way, 回答 can be used as a noun, but here in this specific sentence 答案 is better. Do you know the reason? If not, use your language sense and try to make it out.