Each time your player gets a kill, set KillCount to KillCount + 1, and then you can use Switch on Int for KillCount to do certain things based on whether or not they have a certain amount of kills.
Are you asking for a screen shot of how exactly you need to setup the nodes or jist the logic on how to make things work?
We can help with the second. The first, you probably need someone knowledgable beside you since debugging things is very specific and case by case and a major pain to coordinate via delayed text chat
Make a killcount variable. Make an event dispatcher and event listener associated to a kill event. Whenever theres a kill, retrieve the killer (and the killed if you need death streaks), access the killers killcount variable, increment it and check if it meets a set number of kills, the switch node is a good way to do this quickly and cleanly. Fire the necessary function if the prerequisites are met.