question

You can retrieve players’ profile when calling API GetLeaderboard. As the documentation -- https://docs.microsoft.com/en-us/rest/api/playfab/client/player-data-management/getleaderboard?view=playfab-rest said, you can set the ProfileConstraints field to determine which properties need to be returned in the leaderboard entry. If you want to retrieve the Display Name, you can set the request body as this.

{
    "StatisticName": "Kill",
    "StartPosition": 0,
    "MaxResultsCount": 20,
    "ProfileConstraints": {
        "ShowDisplayName": true
    }
}

Please notice that client API GetLeaderboard can only request the allowed client profile properties. You can allow client access to these properties in the [Game Manage]->[Title Settings]->[Client Profile Option].