How do I see the history of changes on a task?

Open the task and look at the Activity & Discussion panel on the right. It shows comments and changes together, grouped by day.

Good to know

• The panel records actions such as “created this task”, status, priority, date and title updates, assignments, tags, sub-tasks, dependencies, time logged, timers, documents added or removed, emails sent and custom field changes, each with who did it and when.
• Days are labelled Today, Yesterday, or the date.
• The panel shows the most recent 50 changes and the most recent 50 comments.
• Description changes are recorded as “updated description”, but the old text isn’t kept.
• The Last updated time under the project name at the top of the task page shows when the task last changed.
• For a project-wide view, the project’s Dashboard tab has a Recent Activity card listing the 10 most recently updated open tasks, with their assignees, due dates and statuses.