At the top of your dashboard, click the module access icon > Colloboration> blog

The  'Activities' option is available in the blog home page as shown in fig in Fig 1

Note:- To view activities one must need to create blog first. Activity helps to list the others comment on one's blog. 

Fig 1

The Activities option gives us the details of the others comment on our post/blog as shown in the Fig 2

Fig 2

For more information, watch this-