There are 3 ways to regenerate soul points.
You activate the soul point regeneration by killing monsters that gives you an equal amount of experience as you have levels on your character. For example: if your character is level 50 you need to kill a monster that gives you 50 or more experience points or more, a level 100 character needs to kill a monster that gives you 100 experience points or more. Activating the soul points regeneration this way will start a 4 minute timer of regeneration, every new kill with enough experience points will reset this timer back to 4 minutes.
Free account players will regenerate 1 soul point every 2 minutes and premium players will regenerate 1 point every 15 seconds.
Premium players can regenerate soul points by sleeping in a bed, this method will give you 1 soul point every 15 minutes asleep.
The 7 day streak from the daily reward system (from daily shrine) will give you soul point regeneration while in a resting area, such as a depot or house. The regeneration timer is the same as in the first method but does not require monster kills.