One way of finding it is the email address of the office that sent you the citizenship test invite. In my case the invite came from the Hamilton office since I live in Hamilton.
HOWEVER, the Oath email came from the Niagara office. Maybe since the oath ceremony is virtual, there could be some kinda 'load sharing' going on.
Lastly, if everything shows as completed except Oath, that means, they have made a decision to give you the citizenship. Everything is complete and the only thing pending is to wait for the oath invite and do the oath. That can take anywhere between 2 weeks to 2 months after decision made. I waited 2 months. You can see my timelines in the signature.