CB Blogs can be used with Joomla or K2 content. This means you can use sharing extensions for either of those to share blogs. For the internal model you'd need to modify the below template file and directly add your code/HTML for sharing.

components/com_comprofiler/plugin/user/plug_cbblogs/templates/default/blog_show.php

Note it's recommended to copy the default template, delete everything in the copy you do not intend to edit (excluding index.html, leave that), select your new template in CB Blogs > Parameters, then adjust the files you have left as needed.

For CB Activity you'll need to modify the template as well. Sharing features for it are planned in a later release.

Modify the file and simply add it to its output. Review the file carefully. It's best to not modify the default template as suggested above as you will lose your changes when updating CB. I do not recommend modifying PHP files without an IDE like phpstorm (commercial, recommended) or netbeans (free). You'll probably want it add it after the final div of the $return or inside it I suppose if you want it inside of the blogs container div.