Final answer:
The first thing you must do when creating a new dashboard in Cognos Analytics is define data sources.
Step-by-step explanation:
When creating a new dashboard in Cognos Analytics, the first thing you must do is define data sources.
Data sources are the foundation of the dashboard, as they provide the underlying data for the visualizations and analysis.
By defining the data sources, you can connect to various data sets, such as databases, spreadsheets, or web services, and retrieve the necessary information for your dashboard.