Syntax of how to get speed?

Here's a very simple example of how to do this:

using Toybox.WatchUi;
using Toybox.Graphics as Gfx;

class SpeedView extends WatchUi.View {
	var width,height;
	var speed=0.0;
	
    function initialize() {
        View.initialize();
        
        Position.enableLocationEvents(Position.LOCATION_CONTINUOUS, method(:onPosition));
        
		var timer= new Timer.Timer();
		timer.start( method(:onTimer), 1000, true );        
    }
    
    function onPosition(info) {
    	if(info.speed!=null) {speed=info.speed;}
    }
    
    function onTimer() {
    	WatchUi.requestUpdate();
    }

    // Load your resources here
    function onLayout(dc) {
		width=dc.getWidth();
		height=dc.getHeight();
    }

    function onShow() {
    }

    // Update the view
    function onUpdate(dc) {
		dc.setColor(Gfx.COLOR_BLACK,Gfx.COLOR_BLACK);
		dc.clear();
		dc.setColor(Gfx.COLOR_BLUE,Gfx.COLOR_TRANSPARENT);
		dc.drawText(width/2,height/2,Gfx.FONT_SMALL,"speed="+speed,Gfx.TEXT_JUSTIFY_CENTER|Gfx.TEXT_JUSTIFY_VCENTER);
    }

    function onHide() {
    }

}

You need the positioning permission.  In initialize, I start GPS as well as a one second time.  The onPosition callback occurs every second, and the timer is used to update the display every second.

At the end of onPosition, WatchUi.requestUpdate could be called and the timer wouldn't be needed.