A datastore group is all of the datastores where a VMs disks are stored (from documentation: A datastore group consists of the smallest set of datastores required to ensure that if any of a virtual machine's files is stored on a datastore in the group, all of the virtual machine's files are stored on datastores that are part of the same group. For example, if a virtual machine has disks on two different datastores, then Site Recovery Manager combines both datastores into a datastore group.)
There isn't a specific place in SRM to see this all together across SRM, however if you wanted to see it for all VMs you could run a PowerCLI script that looked at the datastores for all VMs protected by SRM. Keep in mind that for ABR you can look at this on a PG basis within SRM.
