@KesireddyNaresh 

On completion of on-demand course content, you will receive voucher to your email and can also be located from ServiceNow University portal from below link

https://learning.servicenow.com/now/lxp/view-all/vouchers/vouchers

Sometimes the voucher might be not available and can be easily fixed by raising a support case with Now Learning team from below link

https://learning.servicenow.com/lxp/en/pages/now-learning-help-center?id=nl_kb_home

Once the voucher is available, go to Web Assessor link and select Register for an Exam, select the exam center and proceed till confirmation or payment page and provide the voucher details and exam will be booked automatically.

As per community guidelines, you can accept more than one answer as accepted solution. If my response helped to answer your query, please mark it helpful & accept the solution.

Thanks,

Bhuvan