Hi K2 Team
Info :K2 tool option list of author Joomla 3.3.6 php 5.5.18

In my case I made two categories in users group . The first one editor and the other author.
I want to show only, users that have permission of author in user group of k2
My problem is that I have both categories, author and editor , in all of categories of articles, so when I select list of autor in k2 tools , shows all.
Thanks and regards
Pablo

imgur.com/gallery/8Vz5V9b/new

You can either show the authors of specific categories (check the module's settings) or you can use the mod_k2_users module and display selected users.