When we open the HANA Cockpit, it always shows a blank page.
The Role sap.hana.admin.roles::Monitoring or sap.hana.admin.roles::Administrator is required to open HANA Cockpit.
If you're opening the cockpit on the system database of a multiple-container, you also need the role sap.hana.admin.cockpit.roles::SysDBAdmin.
You have to assign the role to SYSTEM user manually if you are using SPS9.
Since SPS10 the required roles will be assigned automatically when you log on for first time as the user SYSTEM after database creation.