Whilst worn this item doubles all Smithing xp earned to the rough equivalent of what you'd get in one go from a Large xp lamp, which is also a reward from the Squeal of Fortune (similarly - Prized versions multiply up to Huge lamps).

How much potential you have left can be checked by right-clicking the pendant and selecting the 'check' option, with the original amount depending on your Smithing level (a higher one obviously equating to more claimable xp). After being used-up, this item can either be retained for cosmetic purposes - or recharged using 10 small recharge gems.

Pendants of Skill can be worn in Daemonheim, and sold to the Smuggler for 30 rusty coins, but bear in mind that otherwise this item cannot be dropped or traded - only destroyed. Converting it to coins via the SoF 'claims' menu will provide the player with 15,000.