Garak from Star Trek Deep Space Nine finds himself in Coruscant somehow and someone on the Senate decides to get him to investigate the Supreme Chancellor in order to remove him from the picture.
Who wins? Does Garak outsmart Palpatine by exposing or killing him or does Palpatine kill or get rid of Garak before that happens?
A powerful Sith Lord against a spy posing as a tailor…
Can’t tell if this is a serious question. 
Would Sidious know that Garak was a former Dominion Spy? Garak is even more hidden than Palpatine was(and Palpatine was in the public eye a lot of the time). Palpatine wouldn’t even know he existed as any Senator who found out about his talents(from Garak himself) would tell Garak to keep silent!
One would think that Garak would find out things about Palpatine through contacts and discover he goes off to the lower levels of Coruscant in a hooded black cloak.
He could even learn that Palpatine visits the Bar where Corrupt Senators gamble away their money!
Can he do much else aside from making Corrupt Senators know that Palpatine is watching their actions? Could he turn both Corrupt and Non-Corrupt Senators against him?
Is his spy skills good enough to uncover Palpatine’s Sith identity too?
I think Garak would nope out the moment Sidious offered him a cold glass of root beer.
At the bad guy bar? There’s no way Garak would personally get anywhere near Palpatine in the upper levels(due to being a good spy) and as for his Sidious identity walking around lower Coruscant…
If Garak met Darth Sidious by chance he would recognize him by his lower face as he is a good spy… Of course Darth Sidious meeting him by chance would be unable to read Garak’s mind due to Garak’s discipline so Garak would be able to report Darth Sidious’s identity to his superiors and arrange an exposure by Sidious.
Palpatine could easily be forced to expose his Sith identity as Garak can arrange key attacks at places thus requiring specific Jedi sent there. While many Jedi are distracted Garak can arrange an attack upon the Senate Building forcing Palpatine to draw his Lightsaber to defend himself upon which everyone would see his identity.
Sidious would be forced to flee to Separatist Space and arrange a meeting with the Spy he encountered in Coruscant’s lower levels(who would show no thoughts of being responsible for Sidious’s exposure) and get him to arrange for the use of Order 66.
If Garak wants Sidious completely undermined for the sake of his Senator employer then he’d arrange for Jedi to discover Order 66 in a closed environment then arrange for the Clones to be isolated while removing the chips.
Garak’s chances of winning should Sidious appear in his Darth Sidious identity would raise exponentially. If he never discovers Palpatine is Sidious he simply stirs up distrust against him in the Senate.
In a nutshell, Garak it’s an amazing spy, but Palpatine shoot lighting bolts from his hands.
I remember a conversation that Garak had with the female shape-shifter. He asked if any of his people had survived, but the Founder was short and to the point.
It seems like just about anybody can beat Palpatine if you wait for enough sequels.