Discovery Map Helper Mod v1.2
Download the mod.
Move the downloaded file into your "My Documents\Euro Truck Simulator 2\mod" folder.
Start the game and edit the profile you want to use.
Check the box next to the mod file named "Discovery_Map_Helper" in the panel on the right hand side of the profile edit screen.
Open the world map and look for red roads. Those haven't been discovered yet.