You'll probably want around 20 in both Dex and Spd.
I was able to barely make it with 19.

You'll want to just run and jump off the highest tip of the broken ledge. If you make it enough to at least "stick" to the platform, you'll probably be able to shimmy up the side onto the ledge.
There are more advanced ways to do it, but this guide is not for that.

At some point in the game, if you explore enough..
You'll find the spell Wind Gust.
Using this spell into a sharp incline will catapult you upward.
Lucky for you, the broken ledge serves as one such incline.
You know what to do..

Hope this helped anyone wondering about how many skill points they'd need to actually make the jump without fancy techniques. Have a good day.