Is there any good way to get the current player's speed or player object in minecraft forge 1.19.X

The .getSpeed() method that you found would not do what you want, even if you were able to call it --- it gives you an entity's base speed multiplier, basically how fast do they walk compared to other entities. For player entities, this is hardcoded to 0.1.

However, we can still get the information from the player, we just need to do it in a different way, and to that end you are correct in thinking that we need a reference to the current player. You can always get this via something like

var player = Minecraft.getInstance().player; 

however, I think you might also find that its given to you for free in most places where you'd actually want to use it --- for example, when I was testing this I was just logging out the speed every tick by subscribing to the PlayerTickEvent, and that event gives you the player object directly, so you wouldn't need to grab it yourself.

In any event, we now have a reference to our player --- how do we calculate their speed?

On the player, you'll find a few methods to get their X, Y and Z coordinates in the world: .getX(), .getY() and .getZ(). There are also some fields which store the X, Y and Z position the player was at last frame, these are .xOld, .yOld and .zOld. With this information, we can work out how far the player travelled between this frame and the previous frame.

var deltaX = player.getX() - player.xOld; var deltaY = player.getY() - player.yOld; var deltaZ = player.getZ() - player.zOld; 

^{(In Physics delta, quite literally referring to the Greek letter Δ, means "change", which is why these are named as they are, it's referring to the change in the X, Y and Z values over time).}

Now we have our deltas, how do you calculate the speed? Well, you might remember Pythagoras's theorem from school: a² + b² = c². If you think about a 2d world for a second, we know how far they moved horizontally (their X delta), and how far they moved vertically (their Y delta), so that means that we now have two sides of a triangle (A and B), and to find the total distance that they moved you'd just need to find the third side of that triangle (C).

Well, it turns out that Pythagoras's theorem actually generalises to any number of higher dimensions, giving us a² + b² + c² = d² for 3d spaces. This means that to find the total distance they travelled since last frame, we just need to do this:

var speed = Math.sqrt(Math.pow(deltaX, 2) + Math.pow(deltaY, 2) + Math.pow(deltaZ, 2)); 

This is the player's speed, because speed is just the rate of change of an object's position, which is exactly what we've calculated. A value of 1 would mean, for example, that they had travelled one whole block since last frame, 2 would be two blocks, 0.5 would be half a block, etc. I believe that canonically in Minecraft each block is 1 meter cubed in size, so it would be correct to say that this value is their speed in meters.