Les, SketchUp doesn't have a native angle dimensioning tool. You can measure angles with the protractor tool and then draw in the arc and use leader text to enter the angle. Hold the Alt key and type 0176 on the numeric keypad on the right end of your keyboard. that will give you the degree sign (°).
There is a plugin that was available to create the angle text but I'll have to look for it and see if it is still around.
I'll let you know.