Protractor
You can use the protractor to measure the angle between two lines, then place the resulting overlay in the sonar view.
Image
The protractor tool measures the angle between a baseline and a second line that intersects the baseline.
In the sonar view, click the point where you want to start the baseline. Click the point where you want to end the baseline. Lock one end of the second line to the baseline. Choose where you want the second line to end.