My sim was at university when he gained Alchemistry Mastery. This usually triggers a opportunity to get the Philosopher's stone reward IF there is are science, arborium and the Vault of Antiquity. University doesn't have this, and neither did Lucky Palms which was his home; if they home world has all the buildings then it triggers it upon return.
Anyway to trigger this? Or am I gonna have to cheat?
No, you don't have to cheat, Emmett. Once you edit your town to have all three buildings, just use the alchemy bench and that will trigger a check for Alchemic mastery, and the opportunity will come up.