We are having a problem with our DM. He suddenly stated that a scholar elf could not even roll a test to try and recognize a creature from the desert because he had never been in the desert. What do you think about that?
There is no universal answer, because it depends on the level of cooperative storytelling in your game: in some games the DM completely provides the world and the players just play their PCs, in some other games both players and DMs provide ideas about how the fantasy world is.
In the first case, the DM decides what knowledge exists and is available to a PC (or even if there is any desert at all in the world).
In the second case, the DM allows players to create their PCs more freely and let the PC's abilities define (at least partially) what exists in the world.
With specific relation to Knowledge skills, the first DM is totally entitled to say to even a PC that is specialized e.g. in geography skills, that there something in the world that she still cannot know at all, simply because maybe no one knows. The second DM is eventually going to let the dice roll decide.
The discussion exists because we have a policy of house rules: they have to be agreed upon by everyone. But he's saying this is not a house rule. It's his interpretation of the book.
Whether it is a house rule vs an interpretation, is probably a house rule itself!
Try to have your group answer the previous question, about how much they want PC's characteristics (and therefore player's decisions) to have a meta-influence in shaping the fantasy world, or if instead they want to allow the DM to have more control over it.
Just keep in mind that more freedom to the players is not always a good thing (in this case, too many cooks can spoil the recipe), so you have to find your suitable compromise.