onJoin(client, options){
this.playerCount ++;

    let newPlayer = {
        id: client.sessionId,
        x: 100,
        y: 100
    }

    this.players.push(newPlayer);

    this.players.forEach(player=>{console.log(player)});
    this.send(client,{
        type: "players",
        list: this.players
    })
}

How will i be able to read this list of objects in construct 3?

It's recommended to keep your map of users in the state (using plain Object instead of Array's), and listen for changes in the state.

Example:

this.state.players = {};
this.state.players[client.sessionId] = { x: 100, y: 100 };

You'd then need to listen for additions and changes on players, using the Listen condition:

• Listen: operation = any, path = "players/:id" (listens for add/remove operations)
• Listen: operation = replace, path = "players/:id/:attribute" (listen for changes on attributes)

There's a discussion on the repository about storing and retrieving entities/players by an id string. I'm not sure yet how to keep that reference on Construct3. Maybe you have some idea?