Debug problem

Hello

I’m writing you from Italy
I’m very newbie of WP and I’ve the same problem as Luigi Amorfini

https://wordpress.org/support/topic/error-in-debug-mode-9/

first of all, I would like to know what’s this problem and why I have it.
Second question, how to solve it? you wrote:

removed function <?php screen_icon() ?>

where is “setting.php” file?

Thank you!

Francesco