As a result of adding subtitles to Minecraft, whoever did so was forced to completely rewrite the sounds.json file. As a result of this, all of the sound arguments used in the /playsound command were changed/altered. So here's a nice up-to-date list of sound arguments for 1.9 (based off of the new up-to-date sounds.json file)!
I've set it up so that all sound arguments that play the same sound as another argument will be directly under the one it duplicates. As an added bit to help everyone know what actually plays what, I've listed the actual sound(s) played by each of the arguments, under the arguments, in >>> teal.
Now here's how you should use the command in-game:
/playsound [sound] [source] @p
All you have to do is replace [sound] with the black sound argument of your choice from the list in the spoiler above. And obviously you can switch out @p for @a, @r, @e, or a specific player name if you want. Here's one of my favorites as an example: /playsound entity.enderdragon.growl master @a.
Now you also probably noticed the new [source] argument that they added to the command. Even though this argument is required for /playsound to work, it only specifies which category the sound should play from. The categories all (mostly) match the ones you would find in your sound options, so it's not very complex whatsoever. Since there are so few of them, I'll even list them out for you here: master, music, record, weather, block, hostile, neutral, player, ambient, and voice. If you want to make sure that the sound is heard, simply use the master argument, since if a player is playing with any sound at all, they'll have to have their master volume on at least slightly.
You can also set specific coordinates, volume, and pitch, but I'm sure you don't need me to explain that stuff. If for whatever reason you actually do need me to, I'm instead going to tell you to look here.
Yep, I'm too lazy to upload my own file (also I couldn't find it ), so this is the best you're getting until they update the wiki. Speaking of which, they still haven't updated the wiki page for sounds.json (I think something might be wrong with it...).
I'm currently working on another version of this list that's setup in a similar style to my old list of sound arguments for 1.8
I'll eventually add it to the main thread once it's done, and hopefully it will be organized slightly better, meaning it should be a bit easier to find whatever you're looking for within the list. It might take a while though, since I'm completely revising everything, with an emphasis on the overall organization of the list.
EDIT: New list is on hold for the time being. I've got other things that need to get done beforehand.