Careful! It doesn't mean "got milk?" as in the ad campaign.
Nor does it mean "do you(the store) have milk? That's an American idiom.
To see if a shop with a Spanish-speaking proprietor has milk for sale, ask "Hay leche?" (aye LAY-chay?) "Hay," (pron. like long "I" in English") plus the word of which you seek, is very useful to ask: is it here? OR are they here?
If the person behind the counter is a pregnant female, asking "Tiene leche?" would mean "Do you have breast milk?" It implies that anyway if one is strictly literal.
Say "Hay leche?"
Customer, wanting a liter of milk: "Tiene leche?"
Clerk, a young pregnant women, blushes and says, "No se." (I don't know.)
Customer does the right thing on the rebound: "Hay leche en esta bodega" ("Is there milk to be had
in this shop?")
--Proprietress: "Si, sen~or. Alli! Alli (ay-YEE)!. "Yes, sir, over there! Over there!"
note from contributor: is there a macro-less way on a keyboard to simulate upside-down exclamation marks and question marks?