Hi Anders •,
Welcome to Microsoft Q&A forum and thanks for using Azure Services.
As I understand, you are unable to find Azure SQL Server as to which Subscription it belongs.
Please try to open Azure Portal and if you know SQL Database/SQL Server Name, you could find details in the overview page like below:
Or you could try to list all SQL Servers present in the Resource Group using Azure CLI command as shown below:
Example: az sql server list --resource-group 'resourceGroupName'
Please try and let us know if this helped.
If not, please share more details so that we can help you.
Thanks