Why the double parenthesis in line 2?

The outermost pair of parens are simply the paired delimiters of the  q// operator; a wide range of delimiters, paired or not, can be used by the various string and regex operators. The inner parens are copied from the string as it was given in the OP.

>perl -wMstrict -le
"my $s = q(foo);
 print qq{'$s'};
 ;;
 $s = q((bar));
 print qq/'$s'/;
"
'foo'
'(bar)'
[download]

See Quote and Quote-like Operators (and also Regexp Quote-Like Operators) in perlop.