A simple option is to declare an interface with just the method you want to check for and then do a type assert against your type like;
i, ok := myInstance.(InterfaceImplementingThatOneMethodIcareAbout)
// inline iface declaration example
i, ok = myInstance.(interface{F()})
You likely want to use the reflect
package if you plan to do anything too crazy with your type; http://golang.org/pkg/reflect
st := reflect.TypeOf(myInstance)
m, ok := st.MethodByName("F")
if !ok {
// method doesn't exist
} else {
// do something like invoke m.F
}