Two completely different things. The Kapos were concentration camp prisoners who were selected to be the "heads" (hence the term "Kapo" cf. Italian "capo") of a group of prisoners, such as a particular block of a camp or a forced labor unit. They had an administrative role as well as serving as the Germans' "enforcers" among the other prisoners. The idea of having prisoners enforce regulations against other prisoners was hardly new or original to the Nazis, having existed before and since; if you have prisoners enforcing discipline on other prisoners, it creates tension between the prisoners and impedes the formation of solidarity among them, which in turn makes it easier to prevent organized resistance. Thus the Kapos were permitted, if not outright encouraged to use violence against their fellow prisoners. Kapos existed throughout the concentration camp system and included both Jews and other categories of prisoners.

The Sonderkommandos were groups of prisoners who were assigned to work in the process of mass murder in the gas chambers. These prisoners were almost exclusively Jewish and were only found in the extermination camps and other camps where gas chambers were operated. They performed roles at all stages of the extermination process, from unloading deportees from the trains, to removing their clothes and shaving their hair, to removing bodies and cleaning out the gas chambers after gassing was completed, to disposing of the bodies by burial or burning (whether in a crematorium or on open pyres). The only part of the process they weren't directly involved in was the actual killing itself. The Sonderkommandos were periodically gassed and replaced with new prisoners from subsequent transports to prevent the formation of resistance among them, and when a camp ceased gassing operations, the Sonderkommando working at that time were usually charged with dismantling the camp, before being sent to another camp and gassed; they were considered "bearers of secrets" (Geheimnisträger) because they had witnessed the extermination operations and the last thing the Germans wanted was surviving witnesses. There was also a special operation involving Sonderkommando prisoners from 1943-1945, known as Sonderaktion 1005, in which the Germans attempted to cover up evidence of the Holocaust by digging up mass graves, burning the bodies, and crushing the bones. Obviously they weren't completely successful in this endeavor but it was a systematic effort by the Germans at covering their tracks.

It should be noted that the German authorities weren't entirely successful in preventing resistance from forming among the Sonderkommandos, and there were three notable cases in which the Sonderkommando prisoners revolted against the Germans, with varying degrees of success. The first was at Treblinka in August 1943, when the Sonderkommando prisoners (and prisoners from the associated labor camp) broke into the German armory and attacked the guards at the gates of the camp; the majority of the prisoners who participated in the uprising were killed, but about 70 (10%) of them were able to either make contact with the Polish Home Army or hide among civilians and survive the war.

The second was at Sobibor in October 1943, where a group of Sonderkommando prisoners led by a core of Soviet-Jewish POWs planned and executed an uprising after being warned by the final Sonderkommando prisoners at Belzec (who were brought to Sobibor to be killed) that they would be liquidated once gassing operations ceased there. The Sobibor prisoners planned to kill most of the German camp personnel (particularly the commanders and guards who were particularly hated) before escaping. They managed to kill a few of the Germans without being detected and were planning to begin the second phase of their plan, a massive revolt against the guards, when the first dead Germans were discovered and the remaining Germans began shooting at the prisoners. Some of the prisoners hadn't been aware of the plan, and the leader of the revolt, Alexander Pechersky, tried to organize the escape somewhat, but the scene became quite chaotic, and a substantial number of prisoners were left behind once order was restored; needless to say they were all killed. 58 prisoners are known to have survived. The camp was shut down on Himmler's orders shortly after the revolt.

The last and perhaps best-known example of a Sonderkommando revolt though was at Auschwitz in October 1944. The original plan had been to smuggle in enough gunpowder to bomb one of the crematoria and destroy it and then escape from the camp, and the prisoners spent several months smuggling in gunpowder via prisoners who were working as forced laborers in a nearby munitions factory. However, the timeline of the revolt got accelerated when the Sonderkommando prisoners were informed that they were about to be liquidated before they could complete their plan, so instead, they used their cached weapons to revolt against the Germans and prisoner Kapos before fleeing the camp. Almost all of the prisoners who escaped were recaptured within a few days and those who either failed to escape or recaptured were killed. This event was famously depicted (with some fictionalization) in the 2015 film Son of Saul, which won the Oscar for Best Foreign Language Film and is, in my opinion, the best fictional/semi-fictional Holocaust film.

Sorry for going on such a long digression there but hopefully that clears up the difference for you.