The house edge percentage is disclosed at the discretion of the software provider and / or casino concerned. Certain software providers offer precise house edge numbers for all of their games to ensure transparency.
Microgaming is a shining example of this and you can easily find these numbers for yourself with a quick search. As for online casinos, that is a completely different matter.
Some websites may offer detailed descriptions of all their games and the percentage of their respective house edges. Others can only publish the RTP in its entirety across the board for a particular website, while others do not make that information public at all. This goes on a case-by-case basis and there are no simple answers dewapoker.
Beating the house edge is not impossible, however, doing it in slots is not possible. There are games where you can optimize your gameplay and reduce the house advantage. Blackjack and video poker are great examples of this because you can apply different strategies to your base game.
However, these games differ from slots in the sense that they allow players to make decisions. The basic strategy in blackjack allows players to reduce the house edge by a significant margin and, if casino profits are low enough, even in their favor.