Data labels are generated from the “category” range. For most chart types that is the same as the x-axis. But for xy-chart and bubble-chart you use a separate column in your data range. In most cased you need to edit the data series, because the wizard often does not get it correctly. The category range is the lowest field in the data series dialog page. But make sure, that the other roles are set proper too. The wizard tends to mix things up, if a category column is included for a xy-chart or bubble-chart.
To view the data label set the chart in edit mode. Then you can use Insert > Data label, or you select a single data series or even a single data point and use the context menu. To show text, you have to select the format ‘show category’ (and of cause have previously entered some text in the additional column) . You cannot move the text freely, but there are some positions to choose from the drop-down list in the format dialog.