Here is the full list of all 45 Final Fantasy VIII achievements. It takes around 100-120 hours to unlock all of the achievements on Windows.
Beat the Omega weapon
Reach level 100
Finish the game
Kill 1000 enemies
Win 100 games of Triple Triad
Complete the PuPu side quest
Unlock Guardian Force Doomtrain
Unlock Guardian Force Eden
Complete the Obel Lake side quest
Unlock Guardian Force Bahamut
Unlock Guardian Force Cactuar
Find Ragnarok
Reach maximum HP
Collect all Timber Maniacs magazines
Unlock Guardian Force Tonberry
Collect all cards
Learn all of Quistis' limit breaks
Learn all of Rinoa's limit breaks
Reach SeeD rank A
Reach maximum Gil
Unlock Guardian Force Alexander
Unlock Guardian Force Cerberus
Reach level 100 with Boko
Acquired an item from Chocobo World
Unlock Guardian Force Pandemona
Upgrade your weapon
Capture a Chocobo
Unlock Guardian Force Leviathan
Kill 100 enemies
Unlock Guardian Force Carbuncle
Unlock Guardian Force Brothers
Get your first salary from SeeD
Unlock Guardian Force Diablos
Unlock Guardian Force Siren
Lose a rare card in a Triple Triad game
Unlock Guardian Force Ifrit
Play Triple Triad
Unlock Guardian Force Shiva
Unlock Guardian Force Quezacotl
Draw (Stock) magic from enemies 100 times
Finish the game with Squall's initial level
Defeat every member of the CC Group
Collect all Weapons Monthly/Combat King/Pet Pals/Occult Fan magazines
Draw magic 100 times from draw points
Kill 10000 enemies