In the real world, we used fiat or physical money in our daily spending. And this physical notes can be use in fraudulence or a so-called Fake Money.
How about in Cryptoworld, is there also a Fake Bitcoin? If there's any, how can we identify it?
There is only "bitcoin". Any coins that say that they are the real bitcoin are the fake bitcoin. Most of the coins that got forked claims that they are real bitcoin. Don't listen to them. If they are the real bitcoin, why they called "bitcoin + something" instead of being "bitcoin"? Lol.
If you are taking about creating fake bitcoin within the bitcoin network, no it is not possible. You can't counterfeit bitcoin (on the same chain) like you can do with fiat currency.