To list all modules where an "execute as" has been specified, you can run the below SQL.

SELECTobjects.type_desc AS ObjectTypeDescription

,objects.type AS ObjectTypeCd

,SCHEMA_NAME(objects.SCHEMA_ID) AS SchemaName

,objects.nameAS ObjectName

,USER_NAME(sql_modules.execute_as_principal_id) ExecAsUserName

,objects.SCHEMA_ID

,sql_modules.execute_as_principal_id

FROMsys.objectsAS objects

JOINsys.sql_modulesAS sql_modules

ON sql_modules.OBJECT_ID= objects.OBJECT_ID

WHEREsql_modules.execute_as_principal_id IS NOT NULL -- Exec As is not "owner"

ANDsql_modules.execute_as_principal_id

COALESCE(objects.principal_id , objects.SCHEMA_ID )