For me it work to choose File->Switch Workspace->Other… and it shows the name of current workspace.
I tried to confirm
“Actually, this shows the last workspace that was closed, not the current workspace. If you are opening and closing several, this is not dependable.“
and I am not able to reproduce it. Each time I get the currently loaded workspace (I was testing on Juno). I also checked sources and in ChooseWorkspaceDialog.java and ChooseWorkspaceData.java, and it looks like it manages simple list of last time opened workspaces which is stored as a RECENT_WORKSPACES key in org.eclipse.ui.ide.prefs file. The workspace name shown in this dialog is the first one from this list.