The scars on his chest art partly from canon and partly from fanon. Damian is shown in the initial Batman and Robin run while he's getting treated at talia's place with an open back, cut in a y-shape. Now, since we know that Talia genetically engineered Damian to be perfect, I suspected he might have similar scars on his chest. I researched the cuts on autopsy corpses and added them into the design to fit this idea. I hope this answers your question!
The blond in the last panel? I'm fairly certain that's Teddy, aka Hulkling from Young Avengers. If I'm right, then the boy with him is Billy, aka Wiccan, also from Young Avengers. They're a gay canon couple.
The scar can be seen in the Batman and Son comic. After the first battle, Talia and Damian run away, with Damian heavily injured. He is shown how he gets patched up by Talia's doctors and has a y-shaped scar on his chest.
Guess the current artists forgot about it, or it got fixed off panel. He's shirtless 3 times in the first 12 B&R issues, and it's not there. Then again, most artists can't even seem to decide on his skin tone or how white/middle-eastern he looks, so it's not like they'd really try too hard to remember. Looked at it again, and the paint picture made me squee.
Yeah, in continuity he lost those scars but I think they give a nice touch to his character. Because the show how Talia wanted a perfect son, a son that was genetically engineered with. Haha, not even his costume stays the same from artist to artist, so I guess it's a matter of interpretation. I love to draw Damian with darker skin. Not terrible dark, just....tanned. It's sad how most comic arrtists seem to just put him on one level with the other bat boys.
And I want those Nightwing boxers. WHY HASN'T DC MADE THINGS LIKE THAT YET? Nightwing hoodies and jackets, boxers, they'd be a big a hit. I don't see what's stopping them. >8| Everybody loves some finger stripes.