API GameTooltip SetInventoryItem

hasItem, hasCooldown, repairCost = 
 Tooltip:SetInventoryItem("unit", invSlot {, nameOnly, hideUselessStats});
This function sets a tooltip widget to display information for the given unit's given inventory slot.
----
;Arguments
:;unit : String - the unit whose inventory should be searched
:;slot : Number - the inventory slot number to search
:;nameOnly : Boolean - Only show following info: name, item level, equipment slot, item type, onUse/Proc/Azerite info, durability, race/class limitations
:;hideUselessStats: Boolean - exclude useless (grey) stats. I.e. agility for a warrior. 
----
;Returns
:;hasItem : Boolean - is there an item at the given slot?
:;hasCooldown : Boolean - unknown
:;repairCost : Number - cost of repairing item 
----
;Example
 --See if the player has head gear and if it is broken
 function HasHeadGear()
 local headSlot = getglobal("CharacterHeadSlot");
 local hasItem, hasCooldown, repairCost =
 MyTooltip:SetInventoryItem("player", headSlot:GetID());
 if ((hasItem) and (repairCost) and (repairCost > 0)) then
 return true;
 else
 return false;
 end
 end
----
;Source
This information was obtained via a Google cached page of a Thottbot index of a now expired official US beta forum post by Angarth. It appears to still be correct.
repairCost info obtained from orginal blizzard lua files (PaperDolFrame.lua and MoneyFrame.lua)