Sorry what you want simply isn’t possible. The game supplies no data that the UI code can use to do this. When LU19 goes live we will be able to show your Buffed DPS but not your real DPS ( real time DPS ).
There are third party programs out there such as Combat Stats that will calculate your, your group members and pets real time DPS and paste it do the clip board so you can paste it into the chat window in game. At the time this is your only option for getting such information into the game.
Combat Stats is the most populer, but not sure if it's being upkepted any more. There are a couple others out that, some free some not so free to use. I suggest googling it or what ever search you use and it should find them.