Data mismatch on Subscriber Database in SQL server transactional replication
Please help me on how can i find for what could have been possibly going wrong where data does not match between both the DB.


You can use tablediff utility to find out the difference in data between your Publisher and Subscriber server.

Check How to run TableDiff utility for ALL replicated tables ? article by Chris Skorlinski on REPLTalk. This blog has all the required scripts that will help you out.

If you have 3rd party tools like redgate schema and data compare, then your life would become much easier.

As to find out what went wrong, you should check if 


replication was changed to have filters applied or some column properties has changed to NOT FOR REPLICATION ?
distribution agent is working fine along with the log reader agent ?
Check where the data is missing -


Is data present in distribution database ?
Is data in distribution database and not in subscriber database ?