There are eight wh-questions, which, what, who, whom, whose, when, where, and why and to this list we usually add how as they are all used to elicit particular kinds of information.
Who does Bob know?
Who broke the vase?
Who is coming?
Who, what, which and whose can all be used to elicit information about the subject or object of the sentence.
Verbs may immediately follow the wh-someone as in the first and second questions. In these cases, wh-word functions as the agentive-subject.
In the first question, do is introduced to carry the tense and number since the wh-word functions as a dative-subject.
Whom can only be used to elicit information about the object of the sentence. Although using whom would be grammatically correct, we normally use who instead because it doesn’t sound so formal.
*Whom are you inviting?
Who are you inviting?
Even if a plural response is expected, the verb remains singular. However, when a plural noun follows, a plural verb is used.
What is needed for this dish?
What are the ingredients needed for this dish?
Which biscuits would you want me to buy?
What kind of work do you do?
When there are only two or three possibilities to choose from, which is normally preferred. When there are an unlimited number of choices, what is used.
The wh-something serves as the objective-subject (the neutral noun affected by the action expressed by the verb). A [-human] noun follows wh-something, and do surfaces.
Which bag do you like best?
*Which cousin do you like best?
Who of your cousins do you like best?
If the optional noun is dropped, it is implied that the noun has been previously mentioned.
Which laptop is better?
Which is better?
Whose indicates possession, and like which and what, can be used with or without a noun as a question word.
Wh-possessive allows [+human] noun follows it.
Whose are these?
Whose cousin are you?
How is the most versatile of the wh-words, and may be followed by adjectives, adverbs, quantifiers, BE, and DO but not by a main verb.
How many questions are you expecting?
How do you wish the report to be made?
How far is it?
How does he like his coffee?
How do you keep in touch?
Wh-place, wh-time, and wh-reason limits itself to BE and DO.
Where does he go? (habitual action)
Where is he going?
When does he come? (habitual action)
When is he coming?
Why aren’t you dressed?
Why doesn’t he talk?
Sources: Rosal, Anita Jueco. Communication Arts 1. Mandaue City: Carangue Printing Corporation, 1998.