wp_send_json erase last value

You don’t need to specify datatype in your AJAX call. Also, WP handles AJAX a bit differently, primarily:

$('#filter_evenement').submit(function(){
 jQuery.ajax({
        url:ajaxurl,
        type:"POST", 
        data : {action: "evenements_filter_function", val1: "value1", val2: "values2"},
        success:function(data){console.log(data);
            var dataArray = jQuery.parseJSON(data);//parse JSON

        },
        fail: function( jqXHR, textStatus, errorThrown ) {  
        }
    });
 });

data has to contain action which specifies the WP AJAX handler function in the backend. You can also pass all values you need to send here (e.g val1, val2) Your evenements_filter_function() is not utilizing any data from AJAX call, it’s just sending a response. But to access the values you’d check $_POST['val1'].