Jake is working for Quaritch (Dramatic Irony)
In the beginning of the film, Jake arrives to work with the scientists at Hell's Gate to learn more about the Na'vi people and the ecology of Pandora. However, he is also enlisted by Colonel Quaritch to help with a military effort to extract unobtanium from the planet. For a time, there is a dramatic irony in the fact that we know Jake is a double agent, but Grace Augustine and the other scientists do not know. This also comes into play when Jake befriends and bonds with the Na'vi. While we know that he is working with the RDA to hatch a plan that goes against the interests of the Na'vi, the Na'vi have no idea.
Jake betrays Quaritch (Situational Irony)
Even though Quaritch promises Jake to fund a surgery that will bring him mobility once again and get him out of a wheelchair, Jake ends up betraying the cause of the RDA when he bonds fully with the Na'vi. Jake arrived at Hell's Gate with no interest in the Na'vi people or their customs, but unexpectedly finds himself well-suited to integrate himself into the tribe, which leads him to completely switch allegiances by the end of the film.
Grace thinks Jake is unqualified (Situational Irony)
Jake not only subverts the expectations of Quaritch, but also of Grace Augustine and the other scientists. When he first arrives at the base, Grace is skeptical that he has anything to offer the Avatar Program. Ironically enough, he not only has something to offer, but he is a key player in preserving the resources of Pandora and Grace's interest in a peaceful relationship with the Na'vi.
Eywa saves the day (Situational Irony)
Before the definitive battle with the RDA forces, Jake goes and prays to Eywa to help them in their battle. Looking on, Neytiri assures him that Eywa never takes sides, and so cannot help them. However, halfway through the battle, the creatures of Pandora come in swarms to help the Na'vi cause, representing the fact that Eywa has heard Jake's prayers and is helping their cause.
