This will notify you when the slot changes with the correct slotId for the slot the item is equipped to or unequipped from.
Lua Code:
local function OnSharedSingleSlotUpdate(bagId, slotId, newItem, itemSoundCategory, updateReason)
if bagId ~= BAG_WORN then return end
end
SHARED_INVENTORY:RegisterCallback("SingleSlotInventoryUpdate", OnSharedSingleSlotUpdate)