Based on the context of the questions provided, the answers would be:
- "This wildness" (referring to the instincts or untamed nature Buck possesses)
- "His children" (referring to Buck's instinctual instincts or connections he has retained despite his domestication)
So the completed statements would read as follows: 3. She had the doctor trait, and she washed and cleaned Buck’s wounds each morning after he had finished his breakfast. (This wildness) 6. In spite of his great love for John Thornton, this still remained alive and active in Buck. (His children)