Basic Forms: Shii-Jo, Makashi, Soresu, Force Channel. Every basic Jedi class learns these at different levels and different order, depending on the class.
Advanced: Ataru, Shien, Niman, Juyo. Each leaned at a different order of Jedi Masters found depending on Class. Learned by Guardian, Sentinel, Weapon Master, Marauder, Watchman, Assassin. Each of these classes learn only three of these four forms, depending on their class, and in which order of Jedi Master found.
Potency, Affinity, Mastery, learned only by Consular, Jedi Master, Sith Lord. All in the same order as Jedi Masters found.
In all, 7 forms are learned by the character, rate and order depending on class.
Here's a link for more detail https://strategywiki.org/wiki/Star_Wars_Knights_of_the_Old_Republic_II:_The_Sith_Lords/Forms