Earlier bloggers use to add a custom reply button in blogger that helped users to reply comments of others but now Blogger has officially added this feature. Its a two level commenting system which means you can’t reply to comments which are added as a reply.
How to Enable Thread Comment System in Blogger ?
Blogger's this new feature has already been enabled on all of blogspot blogs by default however there are certain requirements for this threaded comment system to work properly in your blogspot design.1- First, you need to enable comments feature and it must be in embedded mode. You can just go and apply these settings from Settings > Post and comments section.
2- Your comment feed settings must be set as "Full Feed". You can change/confirm this setting by going to Settings > Other
Its a good move by Blogger however there is still a need of more refine like nested commenting system with more levels to Reply. Hopefully Blogger will improve this updated comment system to meet the latest user requirements.