'Inventory lookup' or simply 'lookup' is the general term for retrieving stock levels of one or more items.
ie. 'Can you please lookup that item to make sure we have enough in stock", 'Can you do an inventory lookup for that chocolate bar. I think we're running low."
You also can use the term 'inventory stocktake' when you are checking/retrieving stock levels. But normally you reserve this term for an action not done very often - perhaps once/twice a year for ordering/taxation/financial bookkeeping reasons.
"We need to do a stocktake soon because the end of financial year is coming up"