[Anaraxes]

The skill would perhaps be better named "Cold Reading", though there's more to Fortune-Telling than that as described in Basic.

Whether or not it's part of Acting or Fast-talk seems to be a question of taste for skill granularity. GURPS is normally pretty fine-grained, with separate skills for everything. Fortune-Telling does however include a lot of information, behavior, and purposes not normally part of FT or Acting. Not all actors can do cold reading; I suspect few of them can. So, it'd be a mandatory specialization -- which really isn't much different than a separate skill. If you wanted to go that route, you might as well change all three into mandatory specs of "Deception". That gravity well will then start tugging on Performance as well. (The place you're most likely to see cold reading in the current day, apart from charlatans, is in a magic act.)

If divination actually works in the setting, then there will be different Advantages and associated skills for those abilities, much as Occultism does not cover the "professional" skills of using actual magical spells or psi abilities. Even if divination is real -- perhaps especially if divination is real -- you may well still have fakers.