First off, /testfor requires some form of target selector. So you'll have to use something like @p or @a before you go into the data tags (curly brackets). For a list of all of those and the different things you can do with them, check out the wiki: http://minecraft.gamepedia.com/Commands ... _selectors

As for the data tags, there are just too many to list here. The wiki has two pages filled with just data tag stuff, one with a lot of things about players and items: http://minecraft.gamepedia.com/Player.dat_Format
and yet another with info on all the other entities and blocks (chests, command blocks, droppers, etc.): http://minecraft.gamepedia.com/Chunk_format

Long story short, don't try to memorize them all. Those pages are always updated, and I keep them bookmarked for if I ever need to use them.