It is in the eastern part of the main map, just as you go into the snowy area from the Bonerock Cavern, west from Shatul Wayshrine.
If you are on the search for this shard, following the guidelines from its name, you are not going to end up well. Even though the frozen world suggest it is found in the snowy area, it is just not enough. There are too many waterfalls here!
The one we are after is rather close to a road. You’ll probably end up wondering this area anyways since there are almost three nearby map markings, one wayshrine, one place of interest and a cavern. Just west from Forlorn Watchtower – place of interest – follow a dead end road. If you pay attention to the surroundings, you’ll spot the skill beacon, shining from, not exactly a waterfall, but from a nearby rock. Shame on you developers for misleading us…