Queens Wood isn’t really worth it. The longest descent takes about 1.5 mins and can only really be done at night. Its a dog walkers place.
There are also some small jumps next to Highgate tube, but again not really worth traveling far to get to.
You can link Parkland Walk, Queens Wood, Parkland Walk extension and Ally Pally into a loop, which is OK for a 40min night ride.
Epping can be good. It was very slippery last night and will be awful after the weekend, but is about the best to be had within riding distance of that part of North London.
Otherwise head out towards Herts on bridleways then try Broxbourne and so on.