the email is created by the /WA_Universal_Email/Email_Templates/verification.php file.
it is purposely created as a plain text email to prevent the email from caught in spam filters.
you can change the URL code:
<?php echo($WAGLOBAL_Root_URL); ?>users_Confirm.php?ID=<?php echo($row_WAATKusers['UserID']); ?>&code=<?php echo($row_WAATKusers['UserVerificationCode']); ?>
to link:
<a href="<?php echo($WAGLOBAL_Root_URL); ?>users_Confirm.php?ID=<?php echo($row_WAATKusers['UserID']); ?>&code=<?php echo($row_WAATKusers['UserVerificationCode']); ?>"><?php echo($WAGLOBAL_Root_URL); ?>users_Confirm.php?ID=<?php echo($row_WAATKusers['UserID']); ?>&code=<?php echo($row_WAATKusers['UserVerificationCode']); ?></a>
but this change will increase the possibility of the email being identified as spam and blocked.