from http://dragonage.wikia.com/wiki/Collections
(I rearranged the list) and cofirmed with a phone call to EA Customer Support Representative just a few minutes ago...
The Fall - The Hinterlands
[X]1 Piece in Winterwatch Tower after climbing up two ladders (Near the elven Relic)
[X]1 Piece in Redcliffe Road by entering a broken tower (and climbing up the ladder- just southwest of the Blood Brothers quest encounter).
[X]1 Piece in the Fort Connor landmark The lower area with the Templars and the Primal Red Lyrium)
[X]1 Piece in a ruined house east of Fort Connor along West Road.
[X]1 Piece in the locked farm house just northwest of Redcliffe Farms Camp.
[X]1 Piece in the Dungeon northwest of Redcliffe Farm Camp in Dead Ram Grove.
[X]1 Piece on top of the Dungeon northwest of Redcliffe Farm Camp in Dead Ram Grove.
[X]1 Piece leaning against the house where you recruit Blackwall in Lake Luthias area (south of Upper Lake Camp).
[X][X]2 Pieces in Valammar. One next to the second gear piece in the Hall of Elders, the other inside of the Vault.
[X]1 Piece at the top of the western tower in the Grand Forest Villa.
[ ]Last Piece is bugged as of 12/25/14. It can be seen via fly cam inside the cliff near the Wolf Den.
the last piece according to the EA CSR he said that according to the information that available to him
the character has to have completed killing the Hinterlands dragon
and then search the Wolf Den (the official region name is Wolf Hollow) it is along the north/south river that runs the length of Hinterlands
the northernmost cave, where earlier you are sent to kill some wolves for Dennit's wife (i think that's how it is played out)
after explaining to him been there, done that....
we had already covered the topic that several of his coworkers (not there today) had completed all 12 mosaic pieces, without cheating, that it's possible
but he and his team acknowledged that the classical #11th and #12th piece (up the hill from the duneon) and (wolf's den) were harder than normal
he was going to submit that I had consulted numerous forums, videos, etc. as well as the rest of the community's awareness of this issue
to the feedback department.... where it goes from there...... I'm not one that expects this stuff to be resolved in the next five minutes, week, or even a month
so, hang in there folks, these games take time.... a lot of folks are not as patient as i am, i understand that. i take months to finish a game usually, and i rarely finish every last nook and crany of a game. I'm a casual player. I'm sorry that this issue is not being resolved to the rest of you folks that play this game at a different pace than i do. you have a right to complain, believe me. good luck, folks hopefully this helps as some small consolation prize
maybe i missed something, like i have to get to skyhold first, and approach hinterlands from the other side.. i'm still finishing up a major fight scene