The US government has told Google to query its location database for any device in the vicinity of certain crimes before. There's no way they're not trying to get Apple to do the same.
If Apple designed they'd crypto system as well as they claim that's not viable at this moment in time, but the government can certainly try.
Anybody can write a subpoena, but Apple is on record as having absolutely no problem telling anyone who does so to go fuck themselves and then backing it up with litigation.
No, because Apple doesn't have the private key of the account holder, and so can't see which rotating codes are associated with that account holder since it's all encrypted.
