How can I insert a Google Adsense AD here?

You can create the answers.php file in the dwqa-templates folder then add the following code to the answers.php file then finds the line 10 to add your Ads.
The code: http://snippi.com/s/09kjyml
You can download the dwqa-templates folder here: https://www.designwall.com/question/change-the-text-from-answer-into-question-in-the-login-form/