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

A. A park.

 
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 4 of Season 1 of Resurrection.
 
Having met Mia LaPierre (a serial killer nicknamed . “Lady Vengeance”) at Leon Prater's mansion, Dexter meets her in the park for a date of sorts, in which she tells him, while they are jogging, that she will answer his questions as long as he can keep up with her.

Dexter first questions her about Leon Prater, and she tells him that she doesn't think he has actually killed anyone himself, but is rather a sick voyeur who “wants to hear all the details” of the serial killers sadistic adventures.

They a break while Dexter buys two bottles of water, then Dexter sits on a bench while fitness buff Mia continues her stretching exercises.

As the conversation continues, they share their histories, with Dexter revealing only a few details about his family background, but Mia telling her full origin story, an uprooted  childhood spent with an irresponsible mother, and how she eventually killed her mother's creepy boyfriend after he sexually abused her young sister.

By the time they're finished, she has invited Dexter back to her place.

 
Q. What is it actually in real life?

A. A park.

Q. Where can I find it in real life?

A. This is New York's famous Central Park, the same park where they filmed the earlier scene of Charley picking up Dexter in the park, but not in the same place in the park.   

Central Park is so huge that you'll need more specific info to find this particular spot.

They filmed these early jogging scenes on the southern portion of of The Mall, a broad, straight pathway which runs about 1,400 feet from the Bethesda fountain on the north to the circular flower garden at its south end (which is flanked by statues of Shakespeare and Columbus) .     

And they filmed the latter scenes of the duo sitting on a bench on the benches just west of the stone Naumburg Bandshell, at the far south end of the Mall.
 
The GPS coordinates of the bandshell are 40°46'21.5"N 73°58'17.1"W.

They shot those bench scenes less than 100 feet west/southwest of the bandshell, at around 40°46'21.5"N 73°58'17.1"W . 

Here is a StreetView showing the approximate location of those benches, and the bandshell in the background

It's about 550 feet south of the Bethesda Terrace (with the angel fountain), which we saw at the start of that scene where Dexter meets Charley in the park.  

 
Here is a matching StreetView of the benches  where they filmed the scene: 
 


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