Any arena map, just open the trigges script with jass shop pro or jass craft and copy the triggers out from it.
If you want them in GUI though, I recomend you make them via using logic since it is one of the easiest systems to make.
Also please introduce yourself.
How do you want your duels triggered anyway? Since there are many ways of triggering duels for example automaticly via background calculations or activly by using an ability or walking on a cricle.