From the picture below, this city has truffles and salt. Truffles have a camp on them and salt has a mine. Why does the scree still say 0 amenities from luxury resources? From what I can tell I did not trade them away, because I can still trade them.
With Civ 6 replacing happiness with Amenities it also changed how that is awarded. You must now improve the tile to gain it's benefit for the amenity and the second thing to note is that ALL of your amenities will be shared across ALL of your cities automatically. So it would appear that overall, you do not have enough.
Hope this helps.
Edit: 1 luxury resource = 4 amenities.