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