Display brightness not show in keyboard shortcuts. Help me pls!
I assume you want to change the keyboard shortcut for display brightness to a different shortcut than the dedicated display brightness key on an Apple keyboard, or else you want to set a custom keyboard shortcut on a non-Apple keyboard for display brightness. That is not possible with the System Preferences in current versions of macOS.

You may use a keyboard re-mapping application such as the free Karabiner Elements. After installing it, open the application and select the "Simple Modifications" tab or the "Function keys" tab if you want to remap the function keys. Choose the key you want to use, then from the right drop-down menu, choose "display_brightness_decrement" (or increment) under the "Media controls" section. 

Additional information is available in the documentation.

Alternatively you can use the commercial application BetterTouchTool, or other simialr keyboard-rempapping applications.