There are a few ways to view data from several projects in a single dashboard.
Query-based widgets: Queries can be defined in any project that target all or select projects. Charts based on these queries can be added to any dashboard. To learn more, see Define a work item query, Query across or within projects.
Burndown and Burnup charts: The Burndown and Burnup charts can be configured for any project and team. Therefore, you can add several of these charts to a single chart and configure them to gain a view of progress across several teams and projects.