Hello Shraddha,
You can choose various functions of HR, like:
Training & Development
Recruitment & Seclection
Performance management System (or specifically performance appraisal)
Compensation
besides these broad topic, you can choose parameters of these functions to do comparative studies, Like:
Training methods and its impact on transfer of training
Individual characteristics and transfer of training
360 degree performance appraisal of particular company
succession planning and its impact on organization effectiveness
Methods of recruitment and its impact on recruitment effectiveness
employee engangement
I hope above topics will help you somehow.
Thanks & Regards,
Neha