Zombies can use swords, skeletons bow and arrows, Illagers axes, piglins crossbows and the player various things.

All creatures above use the model HumanoIdModel, if I have their model I could access the item in your hand. I could do that?

model.rightArm.getChild("sword").xScale = 2 ?

(Other thing, what the name of itemChild? "sworditem"? "stick"? [....])

If I could, what is the class that relates the entitymodel and the itemmodel? does it exist?

Edited November 29, 20222 yr by DouglasRafael

The model reads data from the living entity, which is synced from the server. This is synced whenever it is changed because they are rendered on the client. For items in the inventory that are not always rendered, they are not synced. You can get the item via LivingEntity#getMainHandItem or #getOffHandItem.

Yes, but I wasn't looking to take an item out of inventory, but an item in the player's hand and model it.

For example, the player is holding a sword and has it selected in the hotbar. How do I change the scale of this object?

through the link below I know how to model the player: change rotation, scale and translation OF THE PLAYER BUT NOT OF THE ITEM IN HIS HAND:
https://forge.gemwire.uk/wiki/Custom_Item_Animations

How do I rotate the item in his hand. I tried this below, but I couldn't succeed:
modelItemInHand = modelPlayer.rightArm.getChild("some_unknown_name");

I also tried:
modelItemInHand = modelPlayer.rightArm.getAll

Another thing I've also tried is changing the item model for each distinct override just like the crossbow has the models loaded and unloaded. But this method looks much more complex.

23 hours ago, DouglasRafael said:

How do I rotate the item in his hand. I tried this below, but I couldn't succeed:

That's because items aren't part of the model, it is a layer. Unless you are doing it for an item you own, you would need to replace the layer to do your own rendering or rerender the model itself, both of which would probably cause incompatibilities. Alternatively, you could regenerate all the item models with what you want them to have.