When a mob does an certain animation, is the particle established in blockbench or coding ?

[zinc ember]

You could do it directly within the model, but it will look really weird.

Instead what you can do is set a locator in the mouth of the model, which you can tell a particle to emit at

So yes, you would use something outside of the model to create the particles, but the locator can tell the particles where they should emit from

As for actually using that locator, you could use an animation (or animation controller) to emit particles at that locator

[zinc ember]

The locator is an object within a model, yes.