In GanttPRO, you can work with all the comments from all the projects in the account in the Communication hub from the left sidebar.
It is also possible to view particular comments:
1. In the Activity feed from the left sidebar, when you get a notification about a comment on a task assigned to you and click on it.
2. In the Comments section from Standard fields, by clicking on the dialog icon to the left of the task that has comments.
3. In the Comments field, by opening the Task settings of a particular task.
Remember to enable push and(or) email notifications for comments, to receive a notification every time someone leaves a comment on your task.