Q. What is it supposed to be on the show?

A. A bar.

 
Q. Where is it supposed to be on the show?

A. Somewhere in New York.  

Q. When did we see it on the show?

A. In Episode 1 of Season 2
 
Joey Quinn, Dexter 's former Miami Metro coworker, shows up unexpectedly at Dexter's door.
 
They wind up at this local bar, sharing drinks while they talk. 
 
Quinn proposes a toast to Angel, and says he can't believe that Batista thought Dexter was the Bay Harbor Butcher.
 
He asks Dexter how he  ended up in New York and Dexter says he wanted to be with Harrison, who is NYPD now.  Quinn says he quit Miami Metro and is a private detective now. He says he's working for the families of Prater's victims, trying to find Prater. 
 
But he then mentions the fact that although Prater's macabre collection contained a ton of stuff about Miami serial killers, there wasn't anything about the Bay Harbor Butcher.  It was unclear whether he is just curious about why it was missing, or if he was getting suspicious and was subtly interrogating Dexter.  
 
Thinking he should keep an eye on Quinn, offers to help him in his investigation. 

Q. What is it actually in real life?

A. A bar. 

Q. Where can I find it in real life?

A. In real life, this is the Swift Hibernian Lounge, an authentic Irish pub located at 34 E 4th St, in NoHo, near the East Village, New York.
 
Hibernian was the Romans' name for the Irish, and Swift is named after Irish author Jonathan Swift, best known for Gulliver's Travels. 
 
It is widely said that Swift Hibernian Lounge pours the best Guinness in New York, with an authentic Irish atmosphere (including live Irish music), no distracting TV's, and surprisingly good food. 
 
It's located only one block east of Dexter's gym. 
  
 
Here is a matching StreetView of : 
 

 
Here is an aerial photo of the location.  And here is a map link.