Jouissance is defined a type of sensual pleasure that is heightened in some way, an over-the -top type of pleasure. It is hard to believe that Winston would ever have the opportunity for jouissance in the oppressed society of 1984.
However, even in extremely depressed conditions, people find ways of experiencing pleasure. Of course, his sexual relationship with Julia is an obvious example of physical pleasure, but Winston also finds other ways. First, writing in his diary provides him with the type of pleasure that comes from participating in forbidden activities. The diary represents his link with his own humanity, which has been dwindling away, and provides him with intrinsic pleasure.
Beyond that, the coral paperweight, a forbidden object, represents beauty in the novel. Oceania does not offer much beauty, so this small object, obtained from the prole neighborhood, represents this visual pleasure to Winston.
Finally, Winston and Julia share real chocolate and real coffee while in their secret abode above Mr. Charrington's shop. This deviation from the typical rations provide the sensual pleasure of taste, a sense that has been linked with sexuality in some cases.
While these may not seem over-the-top to most readers, to Winston, they represent a vast departure from his normal life and, thus, jouissance.