Use /petsay (and then your sentence)
Check out the Mastermind guides for a better look at pet control with binds, macros, and other abilities you can make your pets utilize.
I know that but there's no text bubble atop his head when i do that.
There isn't a way to make them use Text Bubbles.
The only viable way is to make them use an emote followed by speech, but it won't include their name, only their base pet name (I.E. Punk, Bruiser, Commando, etc)
That sucks i know i use to talk with my robots once 
They changed, but I can't remember when.
Probably because it cluttered up chat? Dunno why, but it is a downer.
How do i get the pet to talk so every one can see what he says?