I don't think that the other solutions posted take into account any changes to @INC that you might make using $PERL5LIB or use lib.

I'd use the contents of the %INC hash. The keys of the hash are the module names and the values are the corresponding paths. For example:

perl -MCGI -le "print $INC{'CGI.pm'}"
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<http://www.dave.org.uk>

"The first rule of Perl club is you don't talk about Perl club."