(b) Add a scatter layer to the chart and add labels to the scatter symbols. The scatter symbols can be set to transparent, so basically you are just adding text. With this method, the (x, y) are in data values (as opposed to pixel coordinates). For example, see:
The above example uses the TextBox.setAlignment method to configure the labels to be on the right side of the symbol. You can use other alignments, such as Chart.Center. The TextBox.setFontAngle can be used to configure the font angles.
(c) If you want to add text on the axis, you can use Axis.addMark. For example: