where can I get the symbol files of Perl? I am using Strawberry Perl

You cannot get them, they are not provided, you have to compile your own perl a "DEBUG build"

when building a Win32 application, and packing it with pp how can I export its symbols for debugging?

pp is just a very small exe that calls libperl, there isn't much to debug --- so just get a debug build of perl then install pp into it, that should work

FWIW, the debugging symbols aren't very useful -- it always comes down to "right, I don't know perl internals" :)