How would you translate: "He asked if the the city had been captured?"
Quaerit num civitatem captum esse?
Here I am using an accusative (captum) plus infinitive (esse).
Am I right?
Thank you!
As an indirect question in subjunctive: "Quaerit an/utrum civitas capta sit."
An indirect question always uses subjunctive (also called conjunctive) in Latin. You just write the question as if it were a normal question, and then change indicative to subjunctive.
An accusative with infinitive cannot be used for indirect questions. Unless the question contains a question word (quis, quando, or similar), an indirect question is often introduced with an or utrum.
The translation suggested by NVaughan is great.