Hello Jaya,
Kindly Mention the Examination Details.
By The way, Every examination board Email/SMS registration No to your registered mobile no/email id. You can search it on your registered Email id.
Otherwise you can request registration No from official website by providing details such as fathers name, DOB etc.
Good Luck.

Hi

Please mention the name of the exam you want to know the application number of.

Is this for JEE Main? Then check your mail and you would also get the application number in each sms sent by CBSE. alternately use the " I cant access my account" option in the login window. Then use the options given therein and then get the application number