i want to add in the slideshow the active dot feature that there is on the don'tmiss item..

ive noticed that the behaviour.js contains script about the dontmiss but not about the slider..
also the slider's li elements don't get an active class so that i could at least make some custom code to add so that on each scroll to have a seperate dot active..

ideally slideshow would consist of 3 elements and corresponding grey dots, changing to red depending on the active li showing

The active dots are css classes which can be found on each K2 Content template.
Also the active class is on the <a> element. Open one of the templates that use the nuSlider script scroll down to the navigation part (almost at the bottom of the php file) and find the pagination's <li> items. There you will also notice the navigationButtonActive class and how these classes are constructed in case you need more than one instance of the slideshow.

i make changes to the default.php at

templates/numuzik/html/mod_nucontent_items/Slideshow

but i see no effect while reloading the page..?? is there a cache issue or am i editing the wrong file?

well no php involved afterall.. just custom.css