Thank you for the provided sample markup and screenshot.
In general, the Chart legend is enabled by setting a value to the [name] property of the SeriesItemComponent:
If the Waterfall chart uses 2 series and the legend is set via the suggested [name] property then the behavior would be as demonstrated in the following example:
But in your example there seems to be only one series, thus I am not sure if the Legend will be a proper solution. Instead, providing a Tooltip for each series item might be a better option.
I hope the provided information helps.
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