The suit of zoom is shown black ....this reminds me of black flash, but it can't be black flash because he is flash hunter and when he touches a scarlet speedster, he dies that very instant. If that would've been the case, Jay Garrick would've been dead by now.
It can't be Jay Garrick's arch nemesis Edward Clariss because his suit has similarities with Jay's suit, and he isn't interested in killing other flashes - he just wants to avenge on Jay for taking away his glorious chance of becoming an unstoppable speedster.
Harrison Wells seems likely to be The Zoom because -
1. The reverse flash with the yellow suit that is Eobard Thawne is also known as Professor Zoom.
In season 1 we saw Harrison Wells saying "that's my cue to leave" when Jay Garrick's helmet came in from the portal. That suggests that he knew about Jay Garrick, which gives an idea that he knew about earth 2 and existence of another speedster.
He could only know all about this if he only visited it. "That's my cue to leave" also gives an idea that Jay Garrick knew about Harrison Wells too.
2. In season 1 before giving the colour to his suit, it was black and the zoom of earth 2 wears a black suit too.
3. In episode 5 of season 2 we saw Harrison Wells giving the idea of creating a speed mirage. If we say that Harrison Wells isn't the reverse how come he was the only one who came up with this idea? Jay , being a speedster, obviously knows more ways to play with the speed than Harrison Wells, but Harrison was the only one to come up with the idea of creating a speed mirage - definitely because he did run at that speed. Don't forget in season 1 he taught Barry how to use his speed in different ways.
4. He knew about Cisco's power, not that he is a metahuman but exactly how his powers works (remember Cisco telling about his powers in season 1 to Harrison Wells).
2) Metahumans of earth 2
1. In season 1 we saw Barry getting a sneak peek in future, this is the when we see Caitlin Snow as Killer Frost. In season 2's episode 5 Caitlin was tested negative for metahuman test courtesy of earth 2's Harrison Wells's metahuman detector watch. That gives an idea that Killer Frost may be from earth 2.
2. We have seen Jay Garrick. In the season finale, we may see a team up of Barry with Jay against Edward(arch nemesis of Jay) with Eobard.
3. As we all recall Plastique died in season 1 there may be another Plastique present on earth 2 who may show up in the upcoming episodes( she is, in all possibility, alive because we have seen her in JLU animated series)
4. In episode 5 of Season 2 Jay Garrick was telling Caitlin about earth 2 where he mentioned Atlantis, so there's a possibility of showing a glimpse of Aquaman or maybe Atlantis. We may see any villian from Atlantis in the upcoming episodes.
3) This theory is a possibility
Maybe Harrison Wells is not reverse but another person following order of Zoom.
In the end of episode 5 of season 2 we saw Wells's daughter chained and kept in a cell where Zoom comes to see her.
Zoom may probably be Eobard Thawne in his original body and he's using Harrison Wells to kill Barry. Harrison is forced to do so in order to save his daughter.
4) This theory is related with DC upcoming movie Batman v Superman
In episode 5 of season 2 Jay mentioned about Atlantis being present on his earth.
In trailer of movie Batman v Superman we saw Aquaman taking steps to unite the seven seas. This brings a thought that the event of movie maybe taking place on Jay's earth and the teamup maybe due to cafighttastrophic events caused by portals acting as bridge between different earths. These portals may have connection with some other planets too, and this may bring Darkseid as an invader coming to conquer earth. Aquaman is uniting the members of Justice League so that they can prepare themselves for their worst fight..!!