At location A on the map provided, you'll meet a knight named Sergeant Kylon. A kindly-yet-distraught man, Kylon has had his hands full recently. An officer in Denerim's order of guards, Kylon has recently had to deal with all sorts of ruffians moving to Denerim to serve in Howe's Denerim-based army. Yet, the nobles sending these troops don't seem to realize that they aren't sending trained soldiers, but complete riffraff, unfit for service, and causing more problems in Ferelden's capital city than solving them. Kylon asks you to head to Denerim's illicit brothel, a place called The Pearl. There, you'll find mercenaries that need taking care of. He wants you to scare them off, and stresses that no one is to be killed.
The Pearl can be accessed via Denerim's map. Thankfully, when you arrive, you'll find that The Pearl isn't exactly a large location. This house of ill repute has little to offer up to you other than the obvious, and the mercenaries you seek should be easy enough to find. They're causing a ruckus in the brothel's main bar. Confront the leader of the mercenaries, and you'll be able to easily threaten them (or persuade them, if applicable) to leave The Pearl. Surprisingly, they do so without much of an issue. After all, they recognize that they are wholly outmatched by a party led by a Grey Warden. Unfortunately, the peace doesn't last for very long.
After you leave The Pearl following the confrontation, the mercenaries you scared off will meet you in a small Denerim-based location called the Back Alley. You'll arrive here automatically no matter where you try to go from The Pearl following the confrontation. You'll run into Sergeant Kylon here, in addition to a detachment of his trusted men. However, in the background, you'll see the mercenaries you just scared off, and now, they want a piece of you. This fight would be hard, except for the fact that you have Kylon and his friends to help you out. Easily lay waste to the angry mercenaries, and Kylon will give you his thanks, and offer to give you more work if you visit him back at location A in the market section of Denerim (on the map located above). Be sure to search the bodies of the downed mercenaries before going about your business, since they no doubt have items and coin for you to acquire.