If its the reef nano cube, it has a small power compact on it, which will support quite a few corals. The problem is anemones and some corals like the frogspawn can get very large and take over your tank.
Look online at the nanopaks of corals and I think you will find some good selections.
As a matter of fact at least one site had beginner nano paks. Whether a clown will go into any of them is another issue. You could find a small Bubble tip, but if it lives, it will get large enough to pretty much take over your tank!