Hi @Hirdesh Baghel,
Per my research, currently there is no such offical document support Get-PnPSubWeb require permission. But in graph api, if you want to list the permission of a site. You will need at least Sites.FullControl.All permission. Please refer to the following document
---If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.