Is XP from challenges/commendations/double XP affected by the daily XP cap?

The Daily Experience Cap applies to all of the above. When it it hit you will get no more experience until the next day. Any commendations or challenges you complete while capped will be forever lost. Double XP is not consumed after hitting the cap though. I'm Currently stuck at 59 and have been hitting the cap every day for the past week. If you get a big payout on experience doing something like spartan ops or just by getting a lot of commendations that match, and you're close to the xp cap, you will only be allowed to gain enough experience to hit the cap and then the leftover is also lost forever. I personally think that commendations and challenges should be exempt from this cap considering you can only accomplish them once, but for now there are no exceptions. once you hit the cap, you're done gaining experience for the day.

Yes, it applies to all of the above.

I can give a source, since I'm rank 56 and have been hitting the cap for the past week now. They fixed it so it doesn't waste your double XP when you are capped. The challenges and commendations though are wasted.