This can be achieved on client side with Lua only, but server side you'd need C++ or else it would be a big, messy hack.
4drik pointed the tooltip thing, that's the right way but it's difficult to work with.
You need something like:
Lua:
function onItemHoverChange(itemWidget, hovered)
if hovered == true then
itemWidget:getTooltip().display()
else
itemWidget.tooltip.hide()
end
end
Somewhere in your scripts, and a tooltip on your otui file.
After that, you need to work out a way to not have to ask the server all the item details when you hover an item, or else the server will be bombarded with requests because players are simply moving their mouses around.