Here's a quick article that I referred to regularly. It shows the location of each scar and how to unlock them.
https://screenrant.com/rogue-legacy-2-scar-locations-guide/One more note: I found completing scars was easier if I checked with Geras in the Drift House every time after selecting a new character. Many scars require attempts with several different characters, so if you make it a habit to visit Geras each time, you'll find it easier to complete.
Also, for all scars except the character-locked ones (like Heavy Weapons), try to complete scars with as *few* empathetic connections as possible. While those make the challenge easier, you are penalized in the final score fpr using them. I completed most scars with only 2-3 empathies.