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