You might have heared of "ArcDPS".
Although Arenanet doesn't like it. there are many addons to the game like ArcDPS that show exactly who and what does the most damage ingame! Figuring out how it works and to install it there are several guides on youtube and on sites like Snowcrows. Visit ArcDPS | Guild Wars 2 Getting Started | Snow Crows for more info and download. There are also options to customize the interface to your liking. Check out this video: (17) Gw2 | How to change the arcdps font - YouTube
Time for pwnage!