Unfortunately, there are no such tools to isolate a single app or a set of apps. QlikView will use as many CPUs and as much RAM as it is available in the system. That's one of the reasons why having several environments (at least development and production) makes a lot of sense.
On the other hand, check the server logs and the Windows event viewer. 6GB in RAM is not that big, if the number of rows and objects is high. It would be an issue if the app only handles 100k rows. Of course, it can be due to poor development but there are applications using a lot more RAM (note that QlikView caches every Qlik, so the more you use the app, the more memory QlikView will use) and that's not a bad thing nor performance is poor.
There is unfortunately no resource logging tied to the app level. Here a a couple of suggestions for indirect approaches.
1. Use the Document Analyzer tool to profile each app. You can further use the DA Compare Tool to aggregate the server RAM requirements for a group of apps.
2. You can do some sluething by loading together the server event, performance and audit logs, sort by time, and see what activities take place between the increases in RAM and CPU reported by the performance logs.