How can I report on all the tasks of a project?

You can use the predefined Project Tasks analysis.

Alternatively, you can create a new analysis using an Oracle Fusion Cloud Project Management subject area that has the Project Name and Task Name dimensions.

For example, you can create an analysis using the Project Control - Budgets Real Time subject area to view all the tasks of a project. If you want to view only those tasks for which project costs exist, then you can create an analysis using the Project Costing - Actual Costs Real Time subject area.