How to handle request key and value in php? [closed]

I want to treat the $ _REQUEST keys and values that a page receives.

The verification would be:

if(!empty($_REQUEST)){
   // Tratamento das chaves e valores
}

That's because I had some security issues, where key values were being changed: (

For this reason I need to do these treatments and I do not know the most efficient way to do it.

To illustrate this, there is a problem printing a $ _REQUEST:

Array
(
    ["onmouseover] => '4Puv(9698)'bad="
)