Irrlicht Engine

Hello,

is it possible to create a game where the world is in 3D, but the characters are 2D sprites?
Like the camera is fixed in a top view and your character is shown as a sprite walking on the game world, colliding with the 3D objects, etc.

Yes

You might want to take a look at billboard SceneNodes.

You mean in the wiki?
Which subtopic should I look for?

No, in the API and examples.