How to print sid value in webform?
The sid won't be available from a validation handler; validation handlers are called before form submission, thus a valid sid for your submission doesn't exist at time of execution. 

If you need to call a post-submit webform hander, the webform module provides hook_webform_submission_insert():

function mymodule_webform_submission_insert($node, $submission) {
  // The submission object contains $submission-&gt;sid, the submission id.
  print_r($submission);
}