Follow the instructions for the CI system you're using.

TeamCity

To display a list of test results including failures, click the Tests tab:

For more details about a specific test, click the  arrow.

TFS using SQL Automation Pack v1.1.0.1765 and later

The file containing test reports is saved in the drop folder you specified when setting up your build definition. To view this in Visual Studio, once your build is complete, click Open Drop Folder:

The test report is saved as <BuildDefinitionName>reports.junit.xml. 

SQL CI command line using SQL Automation Pack v1.1.0.7 and later

When you're using the test step command line options, the output folder for test results is the current working directory unless you include this option in the test step:

/outputFolder="<filelocation>" 

For example:

Test /package=WidgetShop\Database\Output\WidgetShop.1.0.nupkg /temporaryDatabaseServer=(localdb)\v11.0 /outputFolder="c:\WidgetShoptestresults"