Diablo Wiki

Stat Points are acquired when your character levels up. These are used to improve the Strength, Dexterity, Vitality, and Energy of your character. Each level gained earns 5 Stat Points to insert into the Character Attributes.

Stat Points can be gained by:

By level 99, you should have acquired 505 Stat Points if you have completed Alkor's Lam Esen's Tome quest in all three levels of difficulty.