Correct sentence: Who treats animals using a phonendoscope and takes X-ray pictures?
Short answer: A veterinarian, or vet, treats animals. Vets use a phonendoscope (another name for a stethoscope) to listen to an animal's heart and lungs, and they take X-ray pictures to see bones and inside the body.
Why we changed the grammar: In your sentence the verb should match the subject. We use 'treats' and 'takes' (not 'take') because the sentence asks about one person (who), so each verb gets an -s at the end: 'treats' and 'takes.'
Extra simpler sentence: Who treats animals, listens with a stethoscope, and takes X-rays?