A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
Is an item or a spell a legal target for Fingers's action. If i for example have a 3f personality being opposed by a personality with a nasty item or spell, and i want to use Fingers to bow the item or spell.
Battle: Target your unbowed Personality: Target an enemy card. Bow it if its Force is lower than your Personality's Force. If the enemy card's Force is higher, and it has no attachments, destroy your Personality and the enemy card.
Is an item or a spell a legal target for Fingers's action
Yes, an attachment is a legal target for this action's effect if it is in a unit in the current enemy army.
Indeed this Stronghold's action targets an enemy card. Per the glossary, an enemy card is a card in a unit controlled by an enemy player. An attachment is a card in a unit and the Rule of Location reads that it must be in the current enemy army.
Regarding this action's effect on the targeted attachment, Followers have a Force stat but Spells don't have such a stat so use zero instead (see Absent stats). When checking the Force of an Item, use its Force modifier instead, with a minimum of zero (see Card types, Items). At last an attachment is always considered to be a card without attachments (see Card types, Playing attachments).