Final answer:
The Dark Mark is put in the sky three times: during the Triwizard Tournament's Third Task, after the death of Alastor Moody, and at the end of the Battle of Hogwarts.
Step-by-step explanation:
The three times when the Dark Mark is put in the sky are:
- During the Triwizard Tournament's Third Task.
- After the death of Alastor Moody.
- At the end of the Battle of Hogwarts.