If you go east from the Black Heights settlement and follow the river northeast, you’ll soon come to a large waterfall. This is where the falling water meets the natural arch to the west. It’s rather easy to spot this natural arch, as it is massive. The skyshard is on top of the waterfall. To reach this part of the river, you’ll need to go all the way around, following a southern path.
At one point, you’ll pass by some ruins where a Dragon lands. Go around them, and continue downstream. There will be a small waterfall you’ll need to drop down before reaching the big one, and your final destination. Considering this is a remote place, one may question why there is a small camp with a fire east from the waterfall Skyshard. I’ve found a rose inside a small sack there, which might be a part of something that’s better left unsaid.