No, Count Dooku never knew Palpatine planned to replace him with Anakin; he knew Palpatine was Darth Sidious and was privy to most of the grand plan, but he remained oblivious to being disposable, believing he was Sidious's chosen apprentice, only realizing his true worthlessness when ordered to be killed by Anakin in Revenge of the Sith. Dooku's shock and eventual defeat stemmed from this profound betrayal, as he was too trusting and overconfident in his own indispensable role.
We know that Dooku was aware of Palpatine's role in starting the Clone Wars and that he knew Palpatine was Sideous. It's safe to say that Dooku didn't know that Palpatine planned on disposing of him in favor of Anakin.
At one point, Dooku fought Skywalker again on Tythe, but the Jedi failed to defeat the Count. Later, Dooku became apart of Sidious's plan to capture Palpatine during the Battle of Coruscant. However, Dooku was unaware that Sidious's true intentions were for Anakin to kill him and replace him as Sidious's apprentice.
After learning that Palpatine was secretly the Sith Lord Darth Sidious, Dooku turned to the dark side and became a Dark Lord of the Sith himself, replacing Darth Maul as Sidious's second apprentice.
Dooku was an old man, and Anakin was an immensely powerful well of potential that Palpatine had been guiding and influencing since he was ten years old. Dooku was a very useful tool, but didn't fit the long term goals of Palpatine's plan.
In 52 BBY Dooku accompanied Jedi Councilor Jocasta Nu, his friend Sifo-Dyas and his former apprentice Qui-Gon Jinn on a mission to his home world of Serenno to resolve a dispute in the sector. While there, he met the Muun Hego Damask, in reality the Sith Lord Darth Plagueis.
Seems pretty easy to deduce for Ahsoka. She knew there was a dark Lord of the sith who had control of the Senate. Palpatine was disfigured after an attack by the Jedi.
In Universe Reason: Count Dooku already left the jedi order 10 years prior. It is implied that when he learned of Qui-Gon's death, that was the last straw that turned him to the darkside. Going to Qui-Gon's funeral would've exposed Dooku.
Dooku only joined the dark side after Qui gon's death because of the fact he was his apprentice and a close friend and he was pissed at the Jedi order. Watch Tales of the Jedi. Dooku wouldn't have fought Qui-Gon.
During the staged kidnapping of Palpatine, orchestrated by Sidious himself, Grievous was unaware of Palpatine's true identity. In fact, Grievous was prepared to kill the Chancellor if necessary, despite his orders not to, believing that Sidious would forgive him due to the ongoing war.
Palpatines end goal was "power, unlimited power" and to be the eternal god king of all reality. He wanted dominion for the sake of dominion and to have the reach and ability to destroy any opposition to his rule, notably force users.
Plagueis was fully aware Sidious was training Maul as a Sith assassin. Plagueis knew about Maul, Maul suspected Sidious had another master but didn't know for sure. Plagueis had actually intended to end the rule of two with himself and bring back the Sith numbers so he encouraged Sidious.
As far as you know, Anakin Skywalker and Captain Rex were very close friends during the Clone Wars. But before the battle for Coruscant, they had to split up and Rex went with Ahsoka to Mandalore, and Anakin went to Coruscant. After that, Anakin and Rex never saw each other again.
The Lost Twenty, also known as the The Lost, was a name given to the group of twenty Jedi Masters who left the Jedi Order throughout its history. According to Yula Braylon of the Jedi High Council, the Lost Twenty became disillusioned with the Jedi way of life.
He may have been worried about revenge. An alternate theory would be that he just didn't know. Palpatine kept his true identity very secret. He probably only revealed it to Dooku to better lure him to the dark side.
No, Darth Plagueis is not Anakin Skywalker's father; Anakin had no biological father, being born of the Force itself in response to Plagueis's dark side manipulations, with Palpatine's tales of Plagueis's power over life being a manipulation to turn Anakin to the dark side, though Plagueis's attempts to create life did inadvertently cause Anakin's conception.
In Legends, Thrawn had worked with Sidious on the destruction of the Outbound Flight project. The next time they met was decades later, and Sidious had become Emperor. Thrawn probably figured out the Sidious-Palpatine connection right away, and I doubt Sidious would've bothered hiding it.