Take a look at the Player Data Management portion of our Client API: https://api.playfab.com/documentation/client#Player-Data-Management
If you look at GetLeaderboard in particular (https://api.playfab.com/documentation/client/method/GetLeaderboard) you'll see that Leaderboards are tied to player statistics. Getting all leaderboards is just a matter of calling the API for each statistic you track.
If, on the other hand, you're after an call to return a list of all created leaderboards, no, that doesn't exist.
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