Where can I find the Cum Extract?
Viewing post in Gods of Lewdity (Lust Doll Classic mod) comments
You need to go to the Milk Store basement and choose to have your dick and balls milked, if you don't have them you can go to the succubus tower workshop to grow a dick and balls.
(You should try asking questions about the original game here https://indivi.itch.io/lustdoll)