What is undead bone shard
Undead bone shard is an item needed to upgrade hp that estus flask regenerates. To use them you need to use a bonfire in a firelink shrine.
So where to find all undead bone shards.
Undead Settlement
First will be at the Undead Settlement. Near White birch (place where giant archer shooting) turn right and jump at the part separated from cliff undead bone shard will be there.
Cathedral of the Deep
Second, you can find it at the Cathedral of the Deep. It will be near the whtite birch on the gravestone protruding outside the cliff.
Farron Keep
Third will be at the Farron Keep after Keep Ruins bonfire, turn right and go inside a building with slugs undead bone shard will be there.
Catacombs of Carthus
Fourth located at the Catacombs of Carthus. To get it kill hooded skeleton then get undead bone shard from the first skeleton boulder.
Smouldering Lake
\Fifth drops from Carthus Sand Worm in the Smouldering Lake.
Sixth, you can find it in the same location as the fifth. After the bonfire Old King’s Antechamber find a tunnel with 3 Demon Clerics undead bone shard will be at the end of the tunnel
Irithyll of the Boreal Valley
Seventh located at the Irithyll of the Boreal Valley go to the graveyard, after the bonfire Church of Yorshka,then turn right shard will be near Corvian.
Profaned Capital
Eights located near the first bonfire at the Profaned Capital.
Lothric Castle
Ninth will be at the Lothric Castle. Go to the bridge with two wyverns and jump at the cliff on the other side of the bridge.
Grand Archives
Tenth you can get from the corpse on the chair at the top of Grand Archives.