Is there a way to see how top tier DPS distribute their damage among abilities? I am an assassination rogue and I want to understand how the pros damage is distributed. Is it 40% envenom, 20% garrote, 20% rupture and 20% all other?
You’re in the wrong subforum for that 
You can change the forum, to General or Rogue, by editing your post and choosing a diffferent forum.
I’ll give you my quick answer anyway, since you’re here. Rogue is one of those classes I don’t play at all, except I have one to open lockboxes, so I can’t help you of my own knowledge, but I can point you to finding out.
Use WarcraftLogs to look at detailed encounter statistics for Assa Rogues on different types of fights. For example
https://www.warcraftlogs.com/reports/Zmz91GwTNHFknKWM?fight=45&type=damage-done&source=11
https://www.warcraftlogs.com/reports/Zmz91GwTNHFknKWM?fight=24&type=damage-done&source=11
WarcraftLogs is an amazing resource. You can look in detail at all abilities used, all damage taken, all movement on a second-by-second basis. It may take a while to get your head around navigating it, but it has all the information you could ask for.
Thank you! 