With questions like these, perhaps the most general answer is...
in reply to Re^6: The $_ Special Variable
in thread The $_ Special Variable
readily available (USD 30, +//-) from vendors who include the publisher, O'Reilly, and such esteemed booksellers as Amazon, Walmart, and -- very likely -- your local independent bookstore.
Update/afterthought: your OP refers to the symbol pair 'questionmark''underscore'... and so do your further responses when Monks offering help plainly refer to the pair 'dollarsign''underscore'... which is not at all the same thing.
Does your local keyboard omit the "$" sign?