I have found a site Anime Filler List so I want to know that is this real ?
In terms of One Piece, if you click here you will access the anime's wiki page, which clearly separates the arcs and sagas as well as shows which episodes are fillers.
If you type into google "[anime name] wiki story arcs" you should find the arcs, sagas and fillers listed on the page, showing you which episode belongs to which, especially for the more popular and lengthy anime.
As for when to know episodes are filler, you'll know when the episodes go off track with the main goal of the main characters. Fillers can still be fun to watch and if you enjoy the anime, I don't recommend skipping.
One last thing regarding the list you provided. It's probably a good idea to compare these episodes against wiki as well as some other sources to check its authenticity.
Hope this helps!