Access global variable in PHP hook

[Sandra]

Can I access global variable declaired in my php file, to my custom made PHP hook, not tpl hook?

I have tried to catch the value of that variable with $_POST['registrantValue'] from my page. In proba.php I have access to my global variable, but when I try to print the variable in my hook, it always shows that the value is empty. You can see that in the pictures attached bellow.