A debatable point in 1984 could be, “Is it necessary for Winston to die at the end of the book?” On the one hand, it could be argued that Winston, the brain washed person, is already intellectually dead and it is therefore, not necessary to kill him. On the other hand, some may feel that Big Brother would have to kill all people who are guilty of thought crimes in order to preserve power. Either position could be supported.
A "debatable point" is simply one that for which serious/legitimate debate is possible. While it is easy to say that anything could be argued, including the terms "serious" and/or "legitimate" narrow the field considerably. This limits the possible points (or topics) to those for which reasonable claims can be made. For example, imagine that someone has committed a crime. That person is guilty, and even admits it—but it is a first time offense by someone in a desperate situation, such as a single parent stealing a loaf of bread to feed hungry children. One could argue that all crime should be treated the same—a code of strict justice—or one could argue for mercy due to character and circumstance—a code of mercy. The fact that there are two or more sides, supported by facts, makes the point debatable.
If you're looking for one in 1984, I'd have to go with the relative judgment of Winston's actions in Room 101. Was there something else he could/should have done—or was this all that was possible?
A debatable point is an idea that can be apposed or argued. For example, “dogs are popular pets” is not debatable as it is a simple statement of fact. There is no opposing side to the argument. However, “dogs make the best pets because of their warm and friendly nature” is debatable as not every dog has a friendly nature and some people may not agree that dogs make the best pets. In the latter situation, two people could have a “debate” as to whether dogs make the best pets.
From 1984, a possible debatable point may be in the validity of Winston's actions.