Final answer:
Use the Failover Cluster Manager to add additional disk to a Windows Server Failover Cluster Instance for SQL Server cluster. SSMS, Disk Manager, and Server Manager are not designed for this specific task.
Step-by-step explanation:
To add additional disk to a Windows Server Failover Cluster Instance (FCI) for SQL Server cluster, you should use the Failover Cluster Manager. This tool is specifically designed to manage Windows clusters, including adding or configuring storage. The other options provided, such as SSMS (SQL Server Management Studio), Disk Manager, and Server Manager, do not have the functionality to directly manage cluster storage in the context of an FCI.