What kind of action it is to invoke the Legend Lore using a Scholar's Ring, as per its descrtiption? How much studying is required for being able to use this ability? Does observing an object for some time count as studying for the purpose of this ability?
In addition, once every 5 days the wearer can invoke a legend lore spell related to a subject that she has been studying in the previous week, if she has attempted a Knowledge (history) check aided by the ring.
I would think it's a standard action, per rule:
Unless stated otherwise, activating a use-activated magic item is either a standard action or not an action at all and does not provoke attacks of opportunity, unless the use involves performing an action that provokes an attack of opportunity in itself. If the use of the item takes time before a magical effect occurs, then use activation is a standard action. If the item’s activation is subsumed in its use and takes no extra time use, activation is not an action at all.
But normally casting Legend Lore spell is at least 1d4 x 10 minutes, and if you don't have the object in question at hand, it takes either 1d10 days or 2d6 weeks, so shortening it to a standard action is a lot, even if you can use it only once every 5 days.
Activating a ring is usually a std action. However "some rings have unusual activations".