how to show unused variable

I’d like to delete all variables that are declared but never used. I am using Unity 2017.3.1f1 Personal and MonoDevelop.
But Mono does not show those warning messages. I remember that I have seen them before.
I thought that was a default function. But, now, I can’t see those messages no matter what I do.
Can someone help me?

Do you see other warnings? Maybe in the console you disable them to show, click on the top right the triangle icon.