Where were the Kong Skull Island cave paintings?

That's a good question. I'm pretty sure we can rule out Skull Island--I also doubt we'll really get an answer to this question.

But for the sake of speculation, the different shades to each painting/rock makes it seem like they were in different caves, but that seems highly convenient that there were many caves each with a painting of a monster. It was probably the same place, just in different chambers.

 @G.H. (Gman) 

I actually found a possible location. In the Awakening comic (it's canonicity is questionable but this still applies), Serizawa is showing Dr Zamalek Godzilla's historical appearances, he mentions one which is supposedly a cave painting in Chauvet Cave (an actual real cave in France). Funnily enough, one of the Paleolithic drawings it has appear to show "images that have a vaguely butterfly or avian shape to them". Mothra and Rodan?

Wouldn't be surprised if they decided to put that in on the off-chance they would get the rights to the monsters.

Wait....... would Legendary have gotten the rights to use them by that point in production, back when the Godzilla (2014) was being made?

I don't put much stock into the connection with Godzilla: Awakening since I don't consider it canon, but it's an interesting assumption for those who enjoy it I suppose.

And rumor had it Legendary had already grabbed the rights to other monsters when they made the deal with Toho. That's not confirmed, but completely plausible.

actually I think I may have found them it's actually in the U.S. Check out my video for the reasoning Godzilla 2 Cave Paintings Location Found Godzilla 2 MonsterVerse News

Fixed the link for you.