It seems to me that you have, at least, three options.
Owner bob = new() { LastName = "Builder", OwnerID = 1 };
ObservableCollection<Owner> currentOwners = new() { bob };
int idFromIndex = currentOwners[0].OwnerID;
int idFromLinq = currentOwners.Select(owner => owner.OwnerID).FirstOrDefault();
int idFromLinqA = currentOwners.Select(owner => owner.OwnerID).First();