Limit length of slug

At the moment, the plugin does not support to limit the length of the slug question. However, I think you should limit the Question title when submitting a question.
If you want to limit the title, you can open the question-submit-form.php file in the templates/styles/default folder then replace the line code 17 to 22 with the following code:

<form method="post" class="dwqa-content-ask-form" id="form_elem">
 <p class="dwqa-search">
 <label for="question_title"><?php _e( 'Title', 'dwqa' ) ?></label>
 <?php $title = isset( $_POST['question-title'] ) ? $_POST['question-title'] : ''; ?>
 <input type="text" data-nonce="<?php echo wp_create_nonce( '_dwqa_filter_nonce' ) ?>" id="question-title" maxlength="70" name="question-title" value="<?php echo $title ?>" tabindex="1">
 <span id="error_msg" style="color:red"></span>
 <script type="text/javascript">
 $("#validate").click(function(){
 var inputStr = $("#question-title").val();
 if(inputStr.length<70)
 $("#error_msg").html("enter atleast 5 chars in the input box");
 else
 $("#form_elem").submit(); 
 })
 </script>
 </p>