[Solved]-How can i force Highcharts to use same symbols in Legend and Series?-Highcharts

You have to set your marker definitions on the series, not the data.

    {
        "type":"scatter", 
        "name":"s4", 
        "zIndex":9, 
        "marker": {
            "symbol": "diamond"
        },              
        "data":[
            {"x":13.263, "y":35.119}, 
            {"x":16.989, "y":13.021}, 
            {"x":16.2, "y":9.375}
        ]
    }

http://jsfiddle.net/8ma4ts9s/