From ESOUI Wiki
This function returns the index of the outfit slot that the player's current character has equipped. This index will be between 1 and GetNumUnlockedOutfits() if the player has any outfit equipped, or nil if the player has no outfit equipped.
local index = GetEquippedOutfitIndex() if not index then d("You're not wearing an outfit? So unfashionable!") else d(LocalizeString("You're wearing outfit #<<1>>!", index)) end