When i click on Author just below the article TITLE, it links to the K2 Authors profile.
Does it have to link to there or can it link to the persons default joomla profile?
In this case, it would be JomSocial profile.

The link is set to go to the K2 author's page. If you need to change that you will have to modify the item.php page of your K2 template override. If you do not use K2 overrides read here getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates first in order to set them up properly.