In your view I see two data connections. A blue checkmark on DATA1 for the primary then Tableau Engineering and Nursing with an orange checkmark for secondary.
When opening the workbook I see a message that says no relationships are established.
If you go to Data > Edit Relationships you'll see you need to define the blend:
For more information on blending go here: Blend Your Data
To combine data from multiple connections this is the only way to do so.