"Were you reading this book?"
Translation:Czytałeś tę książkę?
No it should not. But you might have heard it. It is sometimes used by some people in colloquial speach
Don't you say : "Czytam właśnie interesującą książkę." so why : "Czytałeś tę książkę"
You mean why 'interesującą' ends with -ą but 'tę' with -ę? On one hand it's logical, because you have tĘ książkĘ. On the other hand, it's different from all the other situatiions, both tamtĄ książkę and forms of adjectives. I guess it's just something that you have to remember. Using "tą" is quite common, but still considered a grammar mistake, so we will not accept it.
What is the difference between 'aś' and 'eś' endings? Does it have to do with gender?