Seldom will you get worse documentation than trying to use the Azure ServiceBus emulator in a real-world scenario. To spare you the frustrations, here's how I translated their docker-compose.yaml reference implementation to something you can actually use as a test fixture in a .NET project.
First, we need 2 containers, one for MSSQL, one for the ServiceBus emulator. ServiceBus emulator uses MSSQL as a backing storage solution. To make things neater, we'll also follow the example docker-compose.yaml file and add an internal network between the two so they don't need to communicate directly over the host's network.
ServiceBus emulator's official
docker-compose.yamlexample file usesazure-sqledge, but it makes no sense to use since it is deprecated and is being phased out. The MSSQL server image works just fine.