Questions without auxiliary verbs

Look at these two questions:
Question word | Auxiliary | Subject | Verb |
Who | do | you | love? |
Question word | verb | object |
Who | loves | you? |
The first question is a normal question and uses the form which we almost always use for a question:
question word + auxiliary + subject + verb
In the second question, the question word is the subject. When the question word is the subject there is no auxiliary verb and the verb agrees with the subject.
Other examples:
Question word | verb | object |
Who | wrote | Romeo and Juliet? |
Who | won | the 2006 World Cup? |
Which player | fouled | Ronaldo? |
What | happened? |
Related pages:
English Grammar Reference: Questions with auxiliary verbs