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