@Ajit
This should work.
You need to go to https://developer.microsoft.com/en-us/graph/graph-explorer#.
On the left side, click on "Sign in with Microsoft" button and login with a user who has at least directory.read permission in your tenant.
Make below call:
GET https://graph.microsoft.com/beta/users/user@yourtenant.onmicrosoft.com/appRoleAssignments
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