If the Jubilee line is not working then the only way to get to the O2 is either by DLR (and then bus) bus, ferry/taxi boat and/or car as the O2 is not served by another tube line.

Boat is the best option really as it literally stops outside the O2.

DLR is possible going to Greenwich and then there taking one of the buses going to the O2. That ride won't take more than 15 mins on a regular day but if it is a weekend day well that could be insane.