The surface marking of the arch of aorta is as follows -
Arch of Aorta surface marking

Right end of sternal angle
Centre of manubrium sterni
Sternal end of left second costal cartilage

These points when connected lies behind the lower half of manubrium sterni.
Behind the manubrium sterni
2nd intercostal space
3rd intercostal space
Left 2nd costal cartilage