This trophy is called "Top Dog", and it's for collecting all 101 Dalmatians within the game. (technically 99, as Pongo & Perdita aren't missing)
These Dalmatians will be sorted out by worlds so you can get them all with minimal visits. And are all located inside of chests.
TRAVERSE TOWN
1, 2, 3 : On the small island behind Merlin's House (Glide ability needed)
4, 5, 6 : Starting alleyway in Traverse Town (Red Trinity Charge needed)
7, 8, 9 : Item Workshop (Green Trinity Ladder needed)
10, 11, 12 : Secret Waterway (Red Trinity Charge needed)
WONDERLAND
13, 14, 15 : Queen's Castle, only reachable through a hidden exit from Lotus Forest, or with High Jump ability.
16, 17, 18 : Lotus Forest, on a raised lilypad (Red Trinity Charge needed)
19, 20, 21 : Tea Party Garden, on balcony (High Jump & Glide abilities are needed)
58, 59, 60 : Lotus Forest, Enter the Bizarre Room from the entrance to the Tea Party Garden. You'll find a picture frame you must activate, and enter, by light the nearby "candles". Once inside, cast Thunder on the string of flowers.
OLYMPUS COLISEUM
22, 23, 24 : Under the statue to the right (Blue Trinity Jump needed)
DEEP JUNGLE
25, 26, 27 : Hippos' Lagoon, on the last islet (Glide recommended, not needed)
28, 29, 30 : Vines 2, climb the vines from Hippos' Lagoon
31, 32, 33 : Waterfall Cavern, in a chest
34, 35, 36 : Camp Area (Blue Trinity Jump needed)
AGRABAH
37, 38, 39 : Treasure Room, in a chest
46, 47, 48 : Palace Gates (High Jump is needed)
49, 50, 51 : Cave of Wonders entrance (High Jump & Glide abilities are needed)
52, 53, 54 : Palace Gates (High Jump & Glide abilities are needed)
HALLOWEEN TOWN
40, 41, 42 : Before Oogie's Manor, on the left side of the bridge
64, 65, 66 : Moonlight Hill, enter the secret green outlined door
67, 68, 69 : Moonlight Hill (White Trinity Detect needed)
70, 71, 72 : Guillotine Square, Glide is needed to enter Pumpkin-like tower
NEVERLAND
43, 44, 45 : Captain Hook's Ship Deck (White Trinity Detect needed)
82, 83, 84 : Ship's Hold, on a beam, use flying to get it
85, 86, 87 : Ship's Hold (Yellow Trinity Push needed)
88, 89, 90 : Captain's Cabin, after AntiSora battle.
MONSTRO
55, 56, 57 : Chamber 3
73, 74, 75 : Mouth (High Jump is needed)
76, 77, 78 : Chamber 6, in a chest
79, 80, 81 : Chamber 5, on one of the higher platforms
HOLLOW BASTION
61, 62, 63 : Grand Hall, left ledge near keyhole, not accessible until 2nd visit
91, 92, 93 : Rising Falls, on top of the water, by the rocks
94, 95, 96 : Castle Gates, cast Gravity on the floating chest
97, 98, 99 : Library, complete the book puzzle and enter the unlocked room, use Gravity spell on the floating chest.
You'll also earn a bunch of rewards upon returning them to Pongo & Perdita in Traverse Town!