The rule as a picture, 5 multiple-choice questions, 3 sentences to correct and a short writing task. Free to print and copy for your class or for self-study.
Want the explanation first? Read the Subject vs Object Questions lesson
When the question word is the subject, use normal order with no do: Who called you? (someone called you). When it's the object, use do / does / did: Who did you call? (you called someone).
Who called you?
Who did you call?
Write two sentences about your own life: one with Subject question and one with Object question. Then explain the difference to a partner.
Answers will vary. Check that each sentence follows the rule on page 1, or paste them into Clarigram to have them checked.