Select subpath

Try this way (CC2018+)

var len = app.activeDocument.pathItems.length;  
  
if (len)  
    {  
    var pth = app.activeDocument.pathItems[len-1];  
  
    pth.deselect();  
    pth.select();  
  
    len = pth.subPathItems.length;  
    var n = prompt("Enter subpath index to select (0-"+(len-1)+")", "0", "");
    var x = -1;
    
    if (n != null) x = Number(n);
    if (isNaN(x) || x < 0 || x > len-1) 
        {
        alert("Bad number");      
        }                       
    else
        {        
        var p = pth.subPathItems[x].pathPoints[pth.subPathItems[x].pathPoints.length-1];  
  
        var zoom = get_doc_zoom();  
  
        //set_doc_zoom(100);  
  
        point_select(p.anchor[0], p.anchor[1]);   
  
        //set_doc_zoom(zoom);  
        }
    }  
else  
    alert("No path");      
  
function point_select(x, y)   
    {  
    var d = new ActionDescriptor();
    var r = new ActionReference();
    r.putClass(stringIDToTypeID("pathComponentSelectTool"));
    d.putReference(stringIDToTypeID("null"), r);
    d.putData(stringIDToTypeID("toolRecordingData"), 
    String.fromCharCode(
        0x00,0x00,0x00,0x06,0x03,0x00,0x00,0x00,0x01,0x00,0x00,0x00,
        0x18,0x54,0x50,0x61,0x74,0x68,0x43,0x6F,0x6D,0x70,0x6F,0x6E,0x65,0x6E,0x74,0x53,0x65,0x6C,0x65,0x63,0x74,0x54,0x6F,0x6F,0x6C,0x00,0x00,0x00,
        0x18,0x54,0x50,0x61,0x74,0x68,0x43,0x6F,0x6D,0x70,0x6F,0x6E,0x65,0x6E,0x74,0x53,0x65,0x6C,0x65,0x63,0x74,0x54,0x6F,0x6F,0x6C,0x00,0x00,0x00,
        0x18,0x54,0x50,0x61,0x74,0x68,0x43,0x6F,0x6D,0x70,0x6F,0x6E,0x65,0x6E,0x74,0x53,0x65,0x6C,0x65,0x63,0x74,0x54,0x6F,0x6F,0x6C,0x00,0x00,0x00,
        0x06,0x3C,0x4E,0x55,0x4C,0x4C,0x3E,0x00,0x00,0x00,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x20,0x20,0x20,0x20,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00)+
        toIEEE754(x, 8, 23) + toIEEE754(y, 8, 23) +  
        String.fromCharCode(0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x01,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00));
  
    executeAction(stringIDToTypeID('toolRecording'), d, DialogModes.NO);  
    };  
  
function set_doc_zoom(zoom)    
    {    
    try {    
        if (!zoom) zoom = 100;    
    
        var d = new ActionDescriptor();      
        var r = new ActionReference();      
        r.putProperty(stringIDToTypeID("property"), stringIDToTypeID("zoom"));      
        r.putEnumerated(stringIDToTypeID("document"), stringIDToTypeID("ordinal"), stringIDToTypeID("targetEnum"));      
        d.putReference(stringIDToTypeID("null"), r);      
    
        var d1 = new ActionDescriptor();      
        d1.putUnitDouble(stringIDToTypeID("zoom"), stringIDToTypeID("pixelsUnit"), zoom/100);  
        d.putObject(stringIDToTypeID("to"), stringIDToTypeID("zoom"), d1);      
        executeAction(stringIDToTypeID("set"), d, DialogModes.NO);      
        }    
    catch (e) { /*throw(e);*/ }    
    }    
  
function get_doc_zoom()    
    {    
    try {    
        var r = new ActionReference();      
        r.putProperty(stringIDToTypeID("property"), stringIDToTypeID("zoom"));      
        r.putEnumerated(stringIDToTypeID("document"), stringIDToTypeID("ordinal"), stringIDToTypeID("targetEnum"));      
        return executeActionGet(r).getUnitDoubleValue(stringIDToTypeID("zoom"))*100;  
        }    
    catch (e) { throw(e); }    
    }    
  
function toIEEE754(v, ebits, fbits)   
    {  
    try {  
        var bias = (1 << (ebits - 1)) - 1;  
      
        var s, e, f;  
        if (isNaN(v))   
            {  
            e = (1 << bias) - 1; f = 1; s = 0;  
            }  
        else if (v === Infinity || v === -Infinity)   
            {  
            e = (1 << bias) - 1; f = 0; s = (v < 0) ? 1 : 0;  
            }  
        else if (v === 0)   
            {  
            e = 0; f = 0; s = (1 / v === -Infinity) ? 1 : 0;  
            }  
        else   
            {  
            s = v < 0;  
            v = Math.abs(v);  
      
            if (v >= Math.pow(2, 1 - bias))   
                {  
                var ln = Math.min(Math.floor(Math.log(v) / Math.LN2), bias);  
                e = ln + bias;  
                f = v * Math.pow(2, fbits - ln) - Math.pow(2, fbits);  
                }  
            else   
                {  
                e = 0;  
                f = v / Math.pow(2, 1 - bias - fbits);  
                }  
            }  
           
        var i, bits = [];  
        for (i = fbits; i; i -= 1) { bits.push(f % 2 ? 1 : 0); f = Math.floor(f / 2); }  
        for (i = ebits; i; i -= 1) { bits.push(e % 2 ? 1 : 0); e = Math.floor(e / 2); }  
        bits.push(s ? 1 : 0);  
        bits.reverse();  
        var str = bits.join('');  
           
        var bytes = "";  
        while (str.length)   
            {  
            bytes += String.fromCharCode(parseInt(str.substring(0, 8), 2));  
            str = str.substring(8);  
            }  
        return bytes;  
        }  
    catch (e) { throw(e); }    
    }