When you run into the middle of the group of five highwaymen conspirators, they'll spring their trap and attack you. Kill them all, then kill the guard and the pair of highwaymen to get your kill count of 8.
NOTE On Test if you died and zoned out the mobs would bug, and be unattackable. If this happens you'll have to delete the quest and start over. Just don't zone out.
Return to Daylia.
Track the "hired assassin" using your tracking and stealth skills North Qeynos.
He's on top of a chain over the bridge ( 416.36, -12.25, -24.52 ) . You must be stealthed to see him.
Knock down the assassin using your range weapon.
NOTE the assassin is a tough fight. You can take him to the guards for assistance.