You ended up on the wrong part of the disABILITIES Board, but here's what you are looking for anyway.
The handicapped viewing areas are marked on all the park maps and when you get to the park, you will see some small signs marking the areas. They do often fill up quite quickly, so plan to be there at least an hour ahead of time if you want to use those areas.
They are:
2 spots by the entrance to World Showcase, sort of behind the gift shops at the entrance to World Showcase, along the water.
In front of Germany, on the Italy side of Germany
Sort of between Canada and the UK
Because the show is viewable from all over the World Showcase, many people choose to find a spot along the fence that surrounds the water. There are some barges parked in the water; the fireworks will be shot off room those barges. Those barges are pulled into place during the afternoon, so you can get a good idea by then where you would be able to see them rom. If you have a good view of the barges, you should have a good view of the show.