I have moved my site http://sarkariresults.yarbook.com to the subfolder http://www.yarbook.com/sarkariresulthindi/
After I moved the site from the sub-domain to the sub-folder, the home page http://www.yarbook.com/sarkariresulthindi/ is working properly, but when I click on a post link, it shows the main domain name content (home page), not the subfolder post.
What could be the cause and how can I fix it?
it's seems you have only moved files and you didn't update the url in your database. You need to apply a search/replace in your database in order to update the url from http://sarkariresults.yarbook.com to http://www.yarbook.com/sarkariresulthindi/. You may do this :
1) using plugin such as https://fr.wordpress.org/plugins/wp-migrate-db/ in the dashboard of your site.
2) accessing phpmyadmin of your site and update the database manually
if both solution didn't work, you may put back your site in the previous subdomain and search in the net How to migrate wordpress site. You will get step by step solutions.
Also don't forget to always go to Permalinks setting and hit save even if there is no changes. It will allow wordpress to update your url structure and edit the htaccess file depending on your new location.
In all the cases it's important to do a backup of your files and databases.