It was 100% most certainly NOT Coruscant. From the novelization, when Rey finds Luke:
The planet was mostly ocean, dotted with a sprinkling of towering islands formed of black rock: the throats of volcanoes whose slopes had long since eroded away. Greenery caped the stony flanks, falling in emerald waves toward the azure sea. Above the calm waters, flying creatures soared on wide wings of translucent white.
Given that Coruscant is basically 100% covered in one large megalopolis, this is definitely a different planet.
The rest of the novelization doesn't really say much about the Temple or the planet it's on.
Also... if it was Coruscant, I severely suspect they wouldn't need a puzzle map to find the bloody capital of the Galactic Empire, would they? :)
UPDATE According to WGA version of the script (confirmed as legit on Reddit), it's most certainly NOT Coruscant and called "AHCH-TO"
EXT. D'QAR - DAY
The Millennium Falcon RISES.
Leia, with Poe, BB-8, and C-3PO (with his proper arm replaced), watches the next generation of Jedi begin her journey.
EXT. SPACE - DAY
The Falcon FLIES through space and BLASTS to LIGHTSPEED.
EXT. AHCH-TO - DAY
A pristine and mighty OCEAN. Endless BLUE, dotted with random, beautiful, mountainous BLACK ROCK ISLANDS, dotted with countless GREEN TREES.
The Millennium Falcon FLIES INTO VIEW, BANKS toward one of the ISLANDS.
In addition, curiously, we hear that there are many Jedi temples, which fits the EU:
Admiral Statura nodded in agreement. “It makes sense. The Empire would have been looking for the first Jedi temples. In destroying all the Jedi sanctuaries they would have acquired a great deal of peripheral information.”
As far as EU, we have several worlds known to have Jedi Temples:
Unclear. I wouldn't say impossible, given Wiki description of the original planet. I wouldn't be surprised if it was the source of the ideas.
However, by 0BBY, it wasn't a match: "the planet was covered by a constant layer of storms, and its surface was the color of ash, with barren plains where immense forests had once stood".
... was ravaged into an arid and toxic planet when the wave struck the planet. Definitely doesn't fit "mostly ocean" (see Wookieepedia picture)
Taris was an ecumenopoly (city-world) like Coruscant. Unlikely.
Raxus Prime was clearly NOT a sight of what could be even remotely called "First" Temple.