The Sitecore license on Azure Paas installations for Sitecore 9.1 is located in the directory /site/wwwroot/App_Data/license.xml
This is true for all the deployed webapps except for the instance appended “-si”
The following webapps also require the license to be installed in an additional location.
xc-search /site/wwwroot/App_data/jobs/continuous/IndexWorker/App_data
ma-ops /site/wwwroot/App_Data/jobs/continuous/AutomationEngine/App_Data
cortex-processing /site/wwwroot/App_Data/jobs/continuous/ProcessingEngine/App_Data