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

A. The DMV (the Department of Motor Vehicles).

 
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 this location in Episode 2 of Season 1 of Resurrection.
 
After Dexter decides to take a job as a Ur-Car rideshare driver (and with Angel Batista having removed Dexter's mistaken death certificate), Dexter goes to the DMV and gets his New York driver's license. It is a very brief scene in which we see him next to the DMV building, looking at his new  driver's license. It reads “Dexter Morgan”, with an address of “77-01 Avenue, Apt 1, Queens, NY. 11385”  
 
( That is, of course, a fake address, meant to be Blessed Kamara's row house. The zip code doesn't even map to Queens, but rather to Glendale, NY, which is about eight miles west of Queens. )

After years of posing as Jim Lindsey in Iron Lake , Dex seems pleased to finally be able to use his real name again.   

 
Q. What is it actually in real life?

A. Just the side of a random office building.

Q. Where can I find it in real life?

A. This was shot right across the street from (east of) “The Oculus”, the mass transit hub at the World Trade Center.
 
The dictionary defines an oculus as “a round or eye-like opening or design, such as a circular window”, and that is precisely what we see here, on the side of this unique transit hub building. All they did is stick a fake DMV sign on the glass.  
 
To let Google AI do the work for once, here's how it describes the Oculus:

The Oculus in New York refers to the striking, white structure located at the heart of the World Trade Center Transportation Hub in Lower Manhattan.     Part of the World Trade Center Transportation Hub: The Oculus is the centerpiece of a major transportation and retail complex at the World Trade Center site.     Designed by Santiago Calatrava: The architect Santiago Calatrava envisioned the structure as a bird taking flight, with its soaring steel ribs and glass panels resembling outstretched wings.     A Hub for Commuters and Visitors: The Transportation Hub, including the Oculus, connects to New Jersey's PATH trains, various New York City subway lines, and provides indoor pedestrian access to nearby buildings like Brookfield Place and the 9/11 Memorial & Museum.     Houses Westfield World Trade Center: The Oculus also houses the Westfield World Trade Center mall, featuring a wide variety of shops and dining options under its unique architecture.     A Symbol of Renewal: The Oculus and the larger Transportation Hub were built to replace the original PATH station destroyed in the September 11, 2001 attacks, and serve as a symbol of hope and resilience for the site.     A Visual Spectacle: The Oculus is known for its breathtaking architecture, characterized by its dramatic, light-filled interior and the unique shape of its "wings". In essence, the Oculus is a remarkable architectural landmark that serves as a transportation hub, retail destination, and a powerful symbol of renewal at the World Trade Center site.

The address of the Oculus is 50 Church Street, New York.  
 
The black building that they are passing off as the DMV seems to be a black tower that houses the  “M Social Hotel” (formerly “The Millennium Downtown” hotel), which is at the northwest corner of Church Street and Day Street, with the address of 55 Church St, New York. 
 
The corner of the building used for that DMV shot appears to be its southwest corner, and the black wall with the DMV sign faces Dey Street. 
 
The green subway entrance visible in the scene is the Cortlandt Street Station, which Is at the same northwest corner of Church Street & Dey Street.It's taking a long time
 
That corner is located about 1,000 feet southeast of the main World Trade Center tower.
 
( For the record, the nearest actual DMV office is almost a mile to the south of the World Trade Center, near Battery Park. )
  
Here is a matching StreetView taken from the same vantage point:


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