A. A downtown luxury hotel. 

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

A.  In New York City.

 
Q. When did we see it on the show?

A. We see it first in Episode 1, of Season 1. 


This is one of the main locations in this season of Dexter: Resurrection, so we see it often, in most episodes.


It's where Dexter's teenage son, Harrison Morgan, is working as a bellhop.
 
It's also where Harrison is living, and where he interacts with various hotel guests and coworkers.
 
And it's where he  accidentally kills a guest named Ryan Foster, a serial rapist, after Harrison catches him about to assault a young woman whom he had drugged at the hotel bar.  When Harrison stops him, they get into a fight, and Harrison bashes his head in with the lid of a toilet tank.
 
Needing to dispose of the body, Harrison falls back on the bloody tactics he learned from his father, back in Iron Lake: He dismembers the body into 9 pieces, and then disposes of them in plastic trash bags by simply putting them on the daily pile of such bags outside the hotel.
 
But that strategy doesn't work well, when workers at the garbage dump discover the body parts , and the police are soon on the case and investigating at the hotel.

Dexter himself shows up eventually, first to observe Harrison from afar, and then to secretly clean up the blood evidence left behind at Harrison's crime scene.


 
The same hotel lobby is used for the scene in Episode 4,  where Angel Batista shows up and talks to Harrison, without revealing to him that Dexter is still alive.

 
Q. What is it actually in real life?

A. A downtown luxury hotel.
 
They not only use the hotel for exterior shots, but used its actual interior as well, including the hotel's stylish lobby and bar.

 

Q. Where can I find it in real life?

A. This scene was filmed at The Empire Hotel, which is located at 44 W. 63rd St, in Manhattan.

The 11-story hotel, which dates back to 1923, contains 426 rooms, in addition to a lobby bar and a rooftop bar.  
 
You will find it at the SW intersection of Broadway & 63rd Street, on New York's Upper West Side, right across the street from Lincoln Center, and just a block west of Central Park. 
 
You can check out the hotel's official website at https://www.empirehotelnyc.com. 
 
( The hotel has been featured on TV before , most notably on Gossip Girl and Power. )

Here is a StreetView from Google:

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