question

>> I want to reset Leaderboard at 20:00 GMT+0 (current time zone of my account) every day via cloud script as a scheduled task but I couldn't find any thread with an example to achieve that.

Currently, we do not suggest using Scheduled Tasks and Cloud Script to reset the leaderboard. We would suggest you call the Admin API IncrementPlayerStatisticVersion regularly on an administrative tool that can run stably to reset the leaderboard using the customize frequencies.

>> I want to give this function parameters of field name and value when it will execute through prize table action but I am not sure how to exactly do that.

To pass the parameters to function, the CloudScript function must contains the incoming parameter args, and we also suggest you reserve the parameter context. Please check our documentation -- https://docs.microsoft.com/en-us/gaming/playfab/features/automation/cloudscript/writing-custom-cloudscript for more information. Please also check the default Revision 1 of your title’s CloudScript (that contains many CloudScript function samples), and the documentations https://docs.microsoft.com/en-us/gaming/playfab/features/data/playerdata/how-to-modify-read-only-internal-player-data, https://docs.microsoft.com/en-us/gaming/playfab/features/automation/actions-rules/using-cloudscript-actions-with-playstream. For your case, the function could be something like this.

handlers.Winner = function (args, context) {
    var fieldName = args.fieldName;
    var fieldValue = args.fieldValue;

    var updateUserDataResult = server.UpdateUserInternalData({
        PlayFabId: currentPlayerId,
        Data: {
            fieldName: fieldValue
        }
    });
    return updateUserDataResult;
};

>> Is it possible to make a cloud function that returns the total number of players in a specific leaderboard when it is called? If yes, I'd appreciate an example.

You can refer to the sample of this thread -- https://community.playfab.com/questions/38373/how-do-you-get-total-number-of-entries-in-a-leader.html to get the total number of players for a specific leaderboard.