No, I'm afraid that's not it. I read about the command in David Pogue's Missing Manual book on the iPhane, and i was using it, but now I've forgotten what it was.
Perhaps I misinterpret it myself, but it sounded to me like the OP was asking about a command to simply bring up Google's voice assistant in a similar way to bringing up Siri--basically when the phone is lying somewhere or even being held just saying some phrase (like "Hey Siri") that would bring up Google's voice assistant.
If it's truly about just opening Google's app using Siri, it's something that I mentioned in my earlier reply, to which the OP responded saying that was not it.
Yes, that's exactly what I meant. The command would open Google to the subject of your question. For example, if you asked a question about the aboriginal population of Australia, the Google app would open with posts on that subject
Yes, that's exactly what I meant. The command would open Google to the subject of your question. For example, if you asked a question about the aboriginal population of Australia, the Google app would open with posts on that subject
Other than that, you can start Siri and then ask Siri to either open the Google app (like "Hey Siri, open the Google app") or do a Google search (like "Hey Siri, google aboriginal population of Australia").