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