What does an ThirdPersonAnimBp inherit from?

I need to use cast to ThirdPersonAnimBP to initiate a shield block animation and don’t know what it inherits from.

If you open your ThirdPersonAnimBP (which I am assuming is an animation blueprint) and click on Class Settings, you will open an editor view with several sections including one that says Class Options. Within Class Options, there should be a Parent Class dropdown, and it will most likely say Anim Instance on it. Unless the dropdown says something else, your ThirdPersonAnimBP inherits from Anim Instance. In C++, the Anim Instance class is known as UAnimInstance (UAnimInstance | Unreal Engine Documentation), but in Blueprint, it is just called Anim Instance.