This may be more than one answer, depending on what is being appraised. Is the following at least reasonable,or am I missing anything?

• Arcana - magic items, spell scrolls, potions (as long as they are identified fully)
• Nature - gems, precious metals
• Religion, History - art (depending on the subject)
• Investigation, Perception - everything else

I should note, I am intentionally trying to make appraisals non-trivial. This likely isn't addressed in the rules because not every DM would do this.