Who saw you?.... Who did you see?

Question 1

\+ Somebody saw Paul.
    ...Who saw Paul?
    ...Silvia. (Silvia saw him.)
    \_\_Who is the SUBJECT
    \_\_Paul is the OBJECT

\+ Silvia saw somebody.
   ...Who DID Silvia see?
   ...Paul. (She saw Paul.)
   \_\_Who is the object
   \_\_Silvia is the subject

Answer 1

In these questions, WHO/WHAT is the SUBJECT:
…Who lives in this house? (= somebody lives in it – who?) (NOT Who does live?)
…What happened? (= something happened – what?) (NOT What did happen?)
…What’s happening? (What’s = What is)
…Who’s got my key? (Who’s = Who has)

In these questions, WHO/WHAT is the OBJECT:
…Who DID you meet yesterday? (= you met somebody – who?)
…What DID Paul say? (= Paul said something – what?)
…Who ARE you phoning?
…What WAS Silvia wearing?

Question 2

Compare:
…George likes oranges.→Who likes oranges? – George.
…What does George like? – Oranges.

Answer 2

…Jane won a new car.→Who won a new car? – Jane.

…What did Jane win? – A new car.