you should use a backend service to store and retrieve your leaderboard data. You can write such a service yourself or use services like GameSparks or PlayFab. Your question basically does not have much to do with Construct.
From your question, it seems to me that you are a novice developer. For this reason, I would recommend learning Construct first. Once you understand what it is for and how to use it, then you'll have a chance of making the integration with backend services you are looking for.