This part is incorrect:
if ( is_single() && ! 'wpdmpro' == get_post_type() )
That essentially means:
if ( is_single() && false == get_post_type() ) {
Which will never be true. To check if a value does not equal another value, use !==
:
if ( is_single() && 'wpdmpro' !== get_post_type() )
Also, the way you’ve combined the two if
statements is hard to read and prone to errors. Instead, just add the first statement as a condition to the one statement:
if ( function_exists('readingtime') && is_single() && 'wpdmpro' !== get_post_type() ) {
echo '<span class="text-sep text-sep-cat">/</span>';
echo readingtime();
}