to quote another sci-fi movie, "did IQs just drop while i was away?" While I am not sure whether I beleive Dooku knows Sidious is Palpatine, the quote you stated bears no relevance on whether Dooku knows or not. If Dooku knew Sidious was Supreme Chancellor, he probably wouldnt help him. Dooku meets SIDIOUS at the end of the movie, not Palpatine. While they are the same person, we have no reason to beleive that Dooku knows, or even that Maul knew. Palpatine is putting on a big show of trying to HELP the Republic. The potential dangers of his rise to power go completely unnoticed by everyone. If everyone else is duped, theres no reason to think Dooku is not. While I'm not sure how I feel about the matter, yet, there is absolutely nothing we know of from the scriptment that suggests Dooku knows.
Why should you? It's just telekinesis. If you can push, pull and throw then you can constrict.
Dooku is a Master; he has a ton of skills alreayd. If he can let his Dark Side emotions flow then he knows pretty much all he needs to know...
...which is not to say he has NOTHING to learn from Sidious, who is obviously superior to just about everyone. That is why he is the Master.
And from what we have seen, you need NO training to let your Dark Side flow! It is, in fact, easier.
Ah, well- if indeed the Sith do have an ability to project their Force use over a great distance...
(and for those who don't know what we are talking about, it was a lin cut from TPM where the Sidious hologram chokes a Neimodian, gloating that only a Sith can use his powers at such range)
... then he would have to be taught that, yes. Still, I doubt that took long.