I'm unsure if this shot of Impus is new footage or not. I don't recognize it from any GoGoV episodes but the columns/pillars don't look like their usual color when it's American footage so I'm presuming this is a Sentai shot.
Here's new footage of Jinxer, Loki, Vypra and Impus
Once you see a close-up of the Dark Trio (aka Demonite, Falkar and Thunderon) feet appearing on grass then it's the start of Sentai footage while they're in the city.
Here's Falkar, Demonite and Thunderon Now this shot looks to be new footage but it's difficult to compare with a shot that's similar to it in the counterpart Sentai episode so I can't make any definite answers in regards to this shot for right now.
Once you see a shot of Falkar with an explosive feather, that's definitely when it's the start of Sentai footage though.
Looks like the footage of the Dark Trio as shown on the Aquabase Monitor is new footage.
Once you see the morphed Red Ranger, it's back to Sentai footage.
The shots of where the explosive Feathers are at are mostly all Sentai footage unless you see civilians in the same shot as the Feathers then it would be new footage.
This shot of the Blue, Green and Yellow Rangers is when it goes back to Sentai footage.
This shot is the start of new footage however this shot is part of that new footage block.
At first I wanted to say that as soon as you see the Dark Trio in the same shot as the Rangers (despite the fact they were currently down but moving) was Sentai footage however I don't see any footage of that specific scene in the GoGoV episode so perhaps that means that it was indeed new footage.
The shot of a feather turning blue and then blowing up while a black background is behind it is actually Sentai footage however the shot of the feather that Ryan flew blowing up is new footage.
The following shots of the Rangers reacting to the explosions likely because of the explosive feathers that were by them is actually new footage.
The shot of the Dark Trio while flames are in front of 'em is likely new footage because I don't see any corresponding footage of that scene in the Sentai episode.
Here's new footage of Demonite
Here's new footage of the Dark Trio in the same shot as the 5 unmorphed Rangers
Here's new footage of Falkar
Here's footage of Ryan being in the Skull Cavern in a strange dream while Diabolico, Jinxer, Vypra and Loki are seen in the Cavern too
All of the Skull Cavern footage that is in Ryan's dream is new footage.

Following info comes from GoGoV Episode 19.
Here's a Demon Card that Diabolico summoned forth from the Hell Mouth
Here's Falkar, Demonite and Thunderon
Here's Demonite.
Here's Thunderon and Falkar
Here's another shot of Falkar
Here's another shot of Diabolico's Dark Trio