Assuming you properly decoded your input,

how does one find out what this stupid thing is

printf("chr(%d)\n",         ord($ch));   # chr(8212)
printf("chr(0x%04X)\n",     ord($ch));   # chr(0x2014)
printf("\"\\x{%04X}\"\n",   ord($ch));   # "\x{2014}"
printf("\"\\N{U+%04X}\"\n", ord($ch));   # "\N{U+2014}"

use charnames ();
printf("\"\\N{%s}\"\n",
    charnames::viacode(ord($ch)));       # "\N{EM DASH}"
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how to regex for it?

$word =~ /\x{2014}/

$word =~ /\N{U+2014}/

use charnames ':full';
$word =~ /\N{EM DASH}/

use utf8;
$word =~ /—/  # Encoded as UTF-8 in the source
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Update: Added crashtest's solution.