Not sure about that link icon. It must have been installed by a plugin, but there are 5 console item icons. They are all .svg sets. ic_envelope, ic_envelopeOpen, ic_notif, ic_user_console, and ic_users_console. They can be found in the images folder of you theme. If you download the image, and open it using Inkscape, you will see two icons in the set; a light color, and a dark color. The dark color will display on hover. To change these you will need to create a new .svg set, and upload it to the images folder using the same name "i.e. ic_user_console" as the image name to overwrite the existing file. I would suggest downloading an icon font set that has .svg images. You can import the new image into the project, and duplicate it so you can make the set. Set the color, size, and placement to be the same as the existing .svg set then you can remove the old icons.

As you can see. it is a bit complicated, but it can be done. Just make sure to have a backup of the original file in case you mess up, or need to start over. There are some tutorials on the web on how to use inkscape.

Not sure about that one. Looking at the cavatar plugin int.php file and another plugin that added  component to the console, they both used the BASE_CMP_console_itemcollector line. They have supporting css files for the items either in the plugin, or in the base css. You can look at the classes in the ow_system_plugins file.

I find not admin icon..all files searches.