As I work in the building directly opposite the terminal across the dock, this is one for me :-)
Please remember the airport doesn’t start having any movements until the afternoon on a Sunday, and even then it’s not as busy as you’ll find it on a weekday.
The best location I know of is along the path that runs between the Connaught Bridge, past the Chinese restaurant/rowing club, the open area with the statue and the Newham Council offices. The eastern end of this is closed for the ABP development works, so you’ll be in the area facing the terminal. Normally the quickest way to get here is on the DLR to Royal Albert, but that branch is closed this weekend so you’ll either need to use the replacement bus from Canning Town or go on the other branch (Woolwich Arsenal trains) to either Pontoon Dock or the airport station itself and then walk round. You’re not supposed to walk over the road bridge, but rather use the footpath under it (from where there is no view of anything).
There may be other locations on the south side of the dock I am not aware of, but the sun will probably be in a better position for photography on that side.
The Sir Steve Redgrave Bridge at the eastern end of the runway (between North Woolwich and Gallions Reach) has the famous view along the runway with Canary Wharf in the background. I go across it several times a week, and if the planes are taking off to the west then you can see them queuing/lining up for takeoff at close quarters.