How do I see which workflows ran and whether they succeeded?

Use the Workflow Execution Logs report (Automation category). It shows every workflow rule execution — the rule name, the triggering record, the execution time, and the success or failure status. Use it to verify that automation is running correctly and to debug any rules that are not firing as expected.

For upcoming scheduled actions, use the Scheduled Time Based Workflow Actions report in the same category.

Learn more about Automation Reports.