do I need Mobile Joomla! & Elegance template

I already have a responsive template for my Joomla, Do I still need Mobile Joomla! & Elegance template for the Kunena mobile Extension?

Yes, the Kunena mobile extension makes use of the Mobile Joomla optimization engine and Elegance template's JQuery Mobile framework, so unfortunately you can't use it on its own.

But what will happen to the look of the other pages appart from joomla, As I already have a responsive mobile aware template I dont want that to change. Just Kunena.

Either you use responsive Joomla template and responsive Kunena theme (because of default themes don't look well on mobile devices), or use Elegance with Kunena Mobile plugin.