Select Angle Annotation toolbar button.

Single-click 3 times to pick arm, vertex and the other arm. If an arm is close to a data point, it will snap to it.

Click angle and drag anchors to adjust.

Mini toolbar for angle and label for common edit.

Double-click angle or right click and choose Properties to see all options.

Double-click to modify the syntax, e.g. $(v, .3) to show 3 decimal places, $(v*pi/180, .2) to convert degree to radian and show 2 decimal places.