I need to find out if my son has post traumatic stress disorder. what are the symptoms?

Get him an eval: Ptsd usually is the result of witnessing or in someway experiencing something that could harm somebody. Symptoms usually fall in 3 domains - re-experiencing (e.G nightmares), hyperarousal (e.g. Jumpiness) and avoidance. However, ptsd symptoms have enough similarities with those of other conditions that i would encourage you to help get him a psychiatric eval so that he can get accurate diagnosis.

PTSD: Great answer by dr. Raina - hit the major points. If he has the types of symptoms she described it is important that he be evaluated sooner rather than later. When left untreated ptsd becomes crustier and more calcitrant to treatment. Who ever evaluates him should have experience in working with ptsd.