Erudin Palace (Slansin)
 

Talking to Toresian will not forcefully spawn him. currently the only way to get him is to wait the normal spawn time, and hope you get the right one

If Slansin is not up, talking to Toresian about 'study enchantment' does respawn him, but it takes 7200 seconds for one of them to spawn.

Point being, keep the fake one up if possible. If someone gives a potion to the real slansin, he will depop and it takes a long time.