Unfortunately, the structure view does not support displaying individual labels.
However, it should be possible to select empty labels using "Tools" -> "Select Elements". To do that, ensure that option "Use These Criteria" is selected on tab "Node Labels" and on that tab only. Empty labels may be selected by setting option "Select" to value "Text", clearing option "Text", and setting option "Match Text" to value "Complete". Other possibilities include selecting labels of pre-selected nodes or selecting labels based on their index (i.e. the first, second, etc. label of a node).