Grammar 
of Wh- Questions

Here're the basic rules again.  What do they require?  What grammar does a student have to be able to handle to carry out this process?
 

Basic Wh- Formation

1. If the question is about the subject of the sentence, insert who or what.

2. If the question is about anything in the predicate or any sub-part of a noun phrase in the subject, (a) insert the correct wh- word, (b) move that word to the beginning of the sentence, (c) move the operator in front of the subject, and (d) add do/does/did if the sentence doesn't have an operator.

 
1. To whom did you send your job application? a. You sent your job application to someone.

b. to is a preposition for a preposition phrase that's an adverbial for direction/place

c. Steps:  insert, move the whole prepositional phrase as a unit, add did to have an operator, change sent to send because only the first word in the verb phrase can have tense

You sent your job application to whom?

To whom you sent your job application?

To whom did you send your job application?

If you move the preposition to the front with the wh- word, you must use whom.

If you leave the preposition at the end and just move the wh- word, you can use who.

Who did you send you job application to?

2. What did you do last summer? You did something last summer.

Do is a pro-verb here--standing in for a full verb with meaning (visited Italy, went to the Beach, took 3 classes). 

The question is about the whole verb phrase: the verb and its direct object.

Steps:

You did what last summer?

What you did last summer?

What did you did last summer?

What did you do last summer?

There's no operator, so did is used.  The resulting question has 2 uses of do for different purposes: (a) operator/auxiliary and (b) full verb/pro-verb. 
What questions do you have? Please email me your questions and comments.