Word order in question with "do you think" and "do you know"
Solution 1:
It might be helpful to note it's not just the location of these two words; they have completely different structure. The first question consists of a single clause. The second has 2 clauses.
Also, the type of answer elicited is different. For "How old do you think I am?" the answer is a number. On the other hand, "Do you know how old I am" is a yes/no question. The statement in (2) would also be a yes/no question, perhaps equivalent of "do you have a guess as to how old I am?"
Solution 2:
The reason for the particular order you have to follow is that questions are formed according to the type they belong to.
The questions below are wh-questions (ref.).
- with an auxiliary
WH-WORD + AUXILIARY + SUBJECT + MAIN VERB …?
- without any auxiliary (when WH-words replace subjects already)
WH-WORD + MAIN VERB …?
How old do you think I am?
Where do you think they went?
What road do you think they followed?
When do you think it'll rain?
How do you think we should do?
Who do you think told them?
The question below are yes-no questions (ref); they are formed differently.
Yes / No questions are the questions which are answered yes or no. It means when we are asking yes/no questions, we are expecting the answer, yes or no.
To form Yes/No questions, we use one of these verbs: auxiliary verbs ( be, do and have ) or modal verbs ( can, may,etc.).
We can not use questions words like what, how, why, who, etc. whilw making Yes/No questions.
Do you know how old I am?
Can you tell where they went?
Will you know what road they followed?
…