They are intended to be eaten with the hands, although a particularly messy hamburger could be approached with fork and knife. Fried chicken is eaten with the hands.
Pizza is eaten with the hands, unless it is too hot or sloppy.
The artichoke is actually the leaf-enclosed flower bud of a plant that is in the thistle family. It is usually served steamed with a dipping sauce. To eat it, pull a leaf off, dip it, scrape the flesh from the base of the leaf with your top teeth, and discard the leaf on the plate provided for that purpose. Switch to fork and knife, first to remove the choke, then to eat the heart and base. Of course, it is also just fine to use a fork and knife to eat asparagus, even when it is perfectly al dente and sauce-free.