How to check what sensitivity label is applied to O365 group via Graph API

In order to check what sensitivity label is applied to O365 group you may go to Azure portal > Azure Active Directory > Groups > select group. Sensitivity label will be displayed in overview tab of the group:

In order to get sensitivity label applied to O365 group programmatically via Graph API you may use the following endpoint:

https://graph.microsoft.com/v1.0/groups/%7BgroupId%7D?$select=assignedLabels

It will return applied label id and display name like this:

{
    "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#groups(assignedLabels)/$entity",
    "assignedLabels": [
        {
            "labelId": "...",
            "displayName": "Private"
        }
    ]

You may test this endpoint e.g. in Graph Explorer: