Translation:Why does he not speak with his mother?
"why he does not speak with his mother"got wrong..guys plz suggest what went wrong here??
Because the sentence begins with "why" you have to change the order of "he does" to "does he"
Assuming you know why you used Dativ: "seiner" is used in combination with a female word "mit seiner Mutter" and "seinem" with a masculine word "mit seinem Vater"
I was wondering the same thing, then i found the answer in this link http://en.wikibooks.org/wiki/German/Grammar/Pronouns
So here "Sein-" is a possessive pronoun, and when it comes with "mit" you need to do the declension thing (der mutter) so you add -er to sein and it becomes Seiner. I hope i understood right, if not can someone correct me plz.