Album de médailles is French for medal album. You can find it at the hotel in Puerto Valor. Once you fill up your first page, you can go to L’Academie De Notre Maitre Des Medailles. There are 55 in act 1, 20 in act 2, and 47 in act 3, for 122 total. You need 75 of them to complete the third page for this achievement (Captain Vize
Here is a guide that says where they all are.https://www.neoseeker.com/dragon-quest-xi/Mini_Medal_Locatio...
These videos show where they all are as well:1-20:
There's also this method if you're post game and don't feel like looking around for them:
Credit for all the videos: Gamer GuruNOTE: You should continue farming them post game if you've finished the medal album in full. The Headmaster will sell you Elfin Elixers for 3 medals and Pep Pips for 10, eliminating the need to purchase them at the casino. You can also win medals by participating in the difficult Black Cup race. You don't even need to win.